Refrigeration apparatus

ABSTRACT

The invention provides a refrigeration apparatus configured to cool the interior of a casing of a heat source unit by a refrigerant. An air conditioner includes a heat source unit, a utilization unit having a utilization heat exchanger and constituting a refrigerant circuit along with the heat source unit, and a controller. The heat source unit causes heat exchange between a refrigerant and a heat source, and cools the interior of the casing, and causes a valve to switch to supply or not to supply the cooling heat exchanger with the refrigerant. The controller assesses, before the refrigerant is supplied to the cooling heat exchanger, whether or not the refrigerant flowing from the cooling heat exchanger toward the compressor comes into a wet state when the refrigerant is supplied, and determines whether or not to open the valve in accordance with an assessment result.

TECHNICAL FIELD

The present invention relates to a refrigeration apparatus, particularlyto a refrigeration apparatus configured to cool the interior of a casingof a heat source unit by means of a refrigerant.

BACKGROUND ART

A refrigeration apparatus includes a heat source unit having a casingthat accommodates equipment such as a compressor and electric componentsthat generate heat while the refrigeration apparatus is in operation. Inorder to cool these types of equipment, the heat source unit may includea fan to cool the equipment with air supplied from outside the casingand discharge air that has cooled the equipment from the casing (e.g.Patent Literature 1 (JP 8-049884 A)).

However, such ventilation may be insufficient and allow excessivetemperature increase in the casing. Particularly in a case where theheat source unit is installed in a room like a machine chamber, thetemperature of the machine chamber, into which the air warmed in thecasing blows, may also rise and, it may adversely affect a workenvironment and the like for a worker in the machine chamber.

SUMMARY OF THE INVENTION Technical Problem

In order to reduce such temperature increase in the casing, the heatsource unit may be provided with a heat exchanger (a cooling heatexchanger) configured to cool the interior of the casing in addition toa main heat exchanger configured to cause heat exchange between a heatsource and the refrigerant, to cool the interior of the casing by meansof a low-temperature refrigerant.

In the case where the refrigerant is supplied to the cooling heatexchanger to cool the interior of the casing, the refrigerant flowingfrom the cooling heat exchanger to the compressor may come into a wetstate under a certain condition to cause liquid compression.

In order to avoid continuous operation of the refrigeration apparatus insuch a state, there may be provided various sensors at a suction side ofthe compressor to detect the wet state of the refrigerant, and therefrigerant may be supplied or may not be supplied to the cooling heatexchanger in accordance with detection results. Such a configuration mayhave risk of at least temporal liquid compression caused by supply ofthe refrigerant to the cooling heat exchanger. Therefore, there is roomfor improvement in terms of reliability of the refrigeration apparatus.

It is an object of the present invention to provide a highly reliablerefrigeration apparatus that is configured to cool the interior of acasing of a heat source unit by means of a refrigerant and can reduce apossibility that liquid compression is caused by supply of therefrigerant to a heat exchanger for cooling the interior of the casing.

Solution to Problem

A refrigeration apparatus according to a first aspect of the presentinvention includes a heat source unit, a utilization unit, and acontroller. The heat source unit includes a compressor, a main heatexchanger, a casing, a cooling heat exchanger, and a valve. Thecompressor compresses a refrigerant. The main heat exchanger causes heatexchange between the refrigerant and a heat source. The casingaccommodates the compressor and the main heat exchanger. The coolingheat exchanger is supplied with the refrigerant to cool the interior ofthe casing. The valve switches to supply or not to supply the coolingheat exchanger with the refrigerant. The utilization unit includes autilization heat exchanger. The utilization unit and the heat sourceunit constitute a refrigerant circuit. The controller controls to openor close the valve. The controller assesses, before the valve is openedto supply the cooling heat exchanger with the refrigerant, whether ornot the refrigerant flowing from the cooling heat exchanger toward thecompressor comes into a wet state when the refrigerant is supplied tothe cooling heat exchanger, and determines whether or not to open thevalve in accordance with an assessment result.

In the refrigeration apparatus according to the first aspect of thepresent invention, it is determined whether to open or not to open thevalve for switching between supply and non-supply of the refrigerant tothe cooling heat exchanger in accordance with the assessment result asto whether or not the refrigerant that flows from the cooling heatexchanger used to cool the interior of the casing toward the compressorwill come into the wet state. This configuration thus achieves a highlyreliable refrigeration apparatus that can reduce the liquid compressioncaused by supply of the refrigerant to the cooling heat exchanger.

A refrigeration apparatus according to a second aspect of the presentinvention is the refrigeration apparatus according to the first aspect,in which the controller assesses whether or not the refrigerant entirelycomes into a gaseous state immediately after flowing out of the coolingheat exchanger when the refrigerant is supplied to the cooling heatexchanger, and determines whether or not to open the valve in accordancewith an assessment result.

According to this aspect, whether or not to open the valve configured toswitch to supply or not to supply the cooling heat exchanger with therefrigerant is determined in accordance with the assessment result as towhether or not the refrigerant entirely comes into the gaseous stateimmediately after flowing out of the cooling heat exchanger. Therefrigeration apparatus thus particularly facilitates reduction ofliquid compression caused by supply of the refrigerant to the coolingheat exchanger.

A refrigeration apparatus according to a third aspect of the presentinvention is the refrigeration apparatus according to the first aspector the second aspect, further including a first deriving unit and asecond deriving unit. The first deriving unit derives first pressureupstream of the valve in a refrigerant flow direction of the refrigerantflowing to the cooling heat exchanger when the valve is opened. Thesecond deriving unit derives second pressure downstream of the coolingheat exchanger in the refrigerant flow direction. The controllerdetermines whether or not to open the valve in accordance with pressuredifference between the first pressure and the second pressure.

Each of the first deriving unit and the second deriving unit to derivepressure is not limitedly configured to derive the pressure inaccordance with a measurement value of a pressure sensor that directlymeasures the pressure. Each of the first deriving unit and the secondderiving unit may alternatively be configured to calculate pressure inaccordance with measured temperature or in accordance with informationsuch as a value of pressure discharged from the compressor or an openingdegree of an expansion valve.

According to this aspect, whether or not to open the valve is determinedin accordance with the pressure difference between the first pressureand the second pressure correlated with quantity of the refrigerantflowing in the cooling heat exchanger when the valve is opened. Thisconfiguration achieves high reliability of the refrigeration apparatusthat can reduce the occurrence of liquid compression.

A refrigeration apparatus according to a fourth aspect of the presentinvention is the refrigeration apparatus according to the third aspect,further including a temperature measurement unit. The temperaturemeasurement unit measures temperature in the casing. The controllerdetermines whether or not to open the valve also in accordance with thetemperature.

According to this aspect, whether or not to open the valve is determinedin accordance with the pressure difference between the first pressureand the second pressure and also the temperature in the casingcorrelated with quantity of heat supplied to the refrigerant in thecooling heat exchanger. This configuration achieves high reliability ofthe refrigeration apparatus that can reduce the occurrence of liquidcompression.

A refrigeration apparatus according to a fifth aspect of the presentinvention is the refrigeration apparatus according to the first aspect,in which the controller assesses whether or not the refrigerant that isobtained after mixing the refrigerant flowing out of the cooling heatexchanger and the refrigerant returning from the utilization unit andthat flows toward the compressor comes into the wet state when therefrigerant is supplied to the cooling heat exchanger, and determineswhether or not to open the valve in accordance with an assessmentresult.

According to this aspect, whether or not to open the valve configured toswitch to supply or not to supply the cooling heat exchanger with therefrigerant is determined in accordance with the assessment result as towhether or not the refrigerant obtained after mixing the refrigerantflowing out of the cooling heat exchanger and the refrigerant returningfrom the utilization unit and flowing toward the compressor comes intothe wet state. The cooling heat exchanger may thus be possibly suppliedwith the refrigerant even under a condition where the refrigerant comesinto the wet state immediately after flowing out of the cooling heatexchanger. The cooling heat exchanger in the present refrigerationapparatus is accordingly applicable under a wider condition.

A refrigeration apparatus according to a sixth aspect of the presentinvention is the refrigeration apparatus according to the fifth aspect,further including a first deriving unit and a second deriving unit. Thefirst deriving unit derives first pressure upstream of the valve in arefrigerant flow direction of the refrigerant flowing to the coolingheat exchanger when the valve is opened. The second deriving unitderives second pressure downstream of the cooling heat exchanger in therefrigerant flow direction. The controller determines whether or not toopen the valve in accordance with pressure difference between the firstpressure and the second pressure and quantity of the refrigerantreturning from the utilization unit.

Also in this aspect, each of the first deriving unit and the secondderiving unit configured to derive pressure is not limited to one thatderives the pressure in accordance with a measurement value of apressure sensor configured to directly measure the pressure. Each of thefirst deriving unit and the second deriving unit may alternatively beconfigured to calculate pressure in accordance with measured temperatureor in accordance with information such as a value of pressure dischargedfrom the compressor or an opening degree of an expansion valve.

According to this aspect, whether or not to open the valve is determinedin accordance with the pressure difference between the first pressureand the second pressure correlated with quantity of the refrigerantflowing in the cooling heat exchanger when the valve is opened and thequantity of the refrigerant returning from the utilization unit. Thisconfiguration thus achieves high reliability of the refrigerationapparatus that can reduce the occurrence of liquid compression.

A refrigeration apparatus according to a seventh aspect of the presentinvention is the refrigeration apparatus according to the sixth aspect,further including a temperature measurement unit and a superheatingdegree deriving unit. The temperature measurement unit measurestemperature in the casing. The superheating degree deriving unit derivesa degree of superheating of the refrigerant returning from theutilization unit. The controller determines whether or not to open thevalve further in accordance with the temperature in the casing and thedegree of superheating of the refrigerant returning from the utilizationunit.

According to this aspect, whether or not to open the valve is determinedin accordance with quantity of the refrigerant and also in accordancewith the temperature in the casing correlated with the quantity of heatsupplied to the refrigerant in the cooling heat exchanger and the degreeof superheating of the refrigerant returning from the utilization unit.This configuration achieves high reliability of the refrigerationapparatus that can reduce the occurrence of liquid compression.

A refrigeration apparatus according to an eighth aspect of the presentinvention is the refrigeration apparatus according to any one of thefirst to seventh aspects, in which the cooling heat exchanger isdisposed on a pipe connecting a pipe connecting between the main heatexchanger and the utilization heat exchanger and a suction pipe of thecompressor.

This configuration achieves high reliability of the refrigerationapparatus that can reduce the occurrence of liquid compression caused bythe refrigerant flowing from the cooling heat exchanger to the suctionpipe.

A refrigeration apparatus according to a ninth aspect of the presentinvention is the refrigeration apparatus according to any one of thefirst to eighth aspects, in which the heat source is water.

According to this aspect, the refrigeration apparatus achieves controlof the temperature in the casing at predetermined temperature even in acase where the refrigeration apparatus utilizes water as the heat sourceand is likely to have heat accumulated in the casing of the heat sourceunit.

Advantageous Effects of Invention

In the refrigeration apparatus according to the first aspect of thepresent invention, it is determined whether to open or not to open thevalve for switching between supply and non-supply of the refrigerant tothe cooling heat exchanger in accordance with the assessment result asto whether or not the refrigerant that flows from the cooling heatexchanger used to cool the interior of the casing toward the compressorwill come into the wet state. This configuration thus achieves a highlyreliable refrigeration apparatus that can reduce the liquid compressioncaused by supply of the refrigerant to the cooling heat exchanger.

The refrigeration apparatus according to the second aspect of thepresent invention particularly facilitates reduction of liquidcompression caused by supply of the refrigerant to the cooling heatexchanger.

The refrigeration apparatus according to each of the third and fourthaspects of the present invention achieves high reliability.

The refrigeration apparatus according to the fifth aspect of the presentinvention can use the cooling heat exchanger, under a wider condition,to cool the interior of the casing.

The refrigeration apparatus according to each of the sixth and seventhaspects of the present invention achieves high reliability.

The refrigeration apparatus according to the eighth aspect of thepresent invention achieves refrigeration apparatus with high reliabilitythat can reduce the occurrence of liquid compression caused by therefrigerant flowing from the cooling heat exchanger into the suctionpipe.

The refrigeration apparatus according to the ninth aspect of the presentinvention achieves control of the temperature in the casing at thepredetermined temperature even in the case where the refrigerationapparatus utilizes water as the heat source and is likely to have heataccumulated in the casing of the heat source unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an air conditioner as arefrigeration apparatus according to an embodiment of the presentinvention.

FIG. 2 is a schematic refrigerant circuit diagram of the air conditionerdepicted in FIG. 1.

FIG. 3 is a schematic side view of the interior of a heat source unitincluded in the air conditioner depicted in FIG. 1.

FIG. 4 is a schematic perspective view of the interior of the heatsource unit in the air conditioner depicted in FIG. 1.

FIG. 5 is a block diagram of a control unit included in the airconditioner depicted in FIG. 1, that particularly shows functional unitsrelevant to control of a first suction return valve included in the heatsource unit.

FIG. 6 is a conceptual graph indicating relations, at differentevaporation temperature levels in a refrigeration cycle, between a flowrate of a refrigerant evaporable in a cooling heat exchanger of the heatsource unit in the air conditioner depicted in FIG. 1 and airtemperature in a casing of the heat source unit.

FIG. 7A is an explanatory diagram on a flow of the refrigerant in therefrigerant circuit in a case where two utilization units each executecooling operation in the air conditioner depicted in FIG. 1.

FIG. 7B is an explanatory diagram on a flow of the refrigerant in therefrigerant circuit in a case where the two utilization units eachexecute heating operation in the air conditioner depicted in FIG. 1.

FIG. 7C is an explanatory diagram on a flow of the refrigerant in therefrigerant circuit in a case where one of the utilization unitsexecutes cooling operation and the other one of the utilization unitsexecutes heating operation in the air conditioner depicted in FIG. 1mainly with an evaporation load.

FIG. 7D is an explanatory diagram on a flow of the refrigerant in therefrigerant circuit in a case where one of the utilization unitsexecutes cooling operation and the other one of the utilization unitsexecutes heating operation in the air conditioner depicted in FIG. 1mainly with a radiation load.

FIG. 8 is an explanatory flowchart of a flow of controlling the firstsuction return valve by the control unit depicted in FIG. 5.

FIG. 9 is a block diagram of a control unit included in an airconditioner according to a modification example A, that particularlyshows functional units relevant to control of a first suction returnvalve of a heat source unit.

FIG. 10 is an explanatory flowchart of a flow of controlling the firstsuction return valve by the control unit depicted in FIG. 9.

FIG. 11 is an explanatory flowchart of a flow of calculating an expecteddegree of superheating by the control unit depicted in FIG. 9.

DESCRIPTION OF EMBODIMENTS

A refrigeration apparatus according to an embodiment of the presentinvention will be described hereinafter with reference to the drawings.The embodiment and modification examples to be described hereinaftermerely exemplify the present invention without limiting the technicalscope of the present invention, and can be appropriately modified withinthe range not departing from the purpose of the present invention.

(1) Entire Configuration

FIG. 1 is a schematic configuration diagram of an air conditioner 10 asthe refrigeration apparatus according to the embodiment of the presentinvention. FIG. 2 is a schematic refrigerant circuit diagram of the airconditioner 10.

FIG. 2 depicts only part of constituents in a heat source unit 100B forsimplified depiction. The actual heat source unit 100B has aconfiguration being similar to a heat source unit 100A.

The air conditioner 10 executes vapor-compression refrigeration cycleoperation to cool or heat a target space (e.g. a room in a building).The refrigeration apparatus according to the present invention is notlimited to the air conditioner but may alternatively be configured as arefrigerator, a freezer, a hot-water supply apparatus, or the like.

The air conditioner 10 mainly includes a plurality of heat source units100 (100A and 100B), a plurality of utilization units 300 (300A and300B), a plurality of connection units 200 (200A and 200B), refrigerantconnection pipes 32, 34, and 36, and connecting pipes 42 and 44 (seeFIG. 1). The connection unit 200A is configured to switch a flow of arefrigerant to the utilization unit 300A. The connection unit 200B isconfigured to switch a flow of the refrigerant to the utilization unit300B. The refrigerant connection pipes 32, 34, and 36 are refrigerantpipes connecting the heat source units 100 and the connection units 200.The refrigerant connection pipes 32, 34, and 36 include aliquid-refrigerant connection pipe 32, a high and low-pressuregas-refrigerant connection pipe 34, and a low-pressure gas-refrigerantconnection pipe 36. The connecting pipes 42 and 44 are refrigerant pipesconnecting the connection unit 200 and the utilization unit 300. Theconnecting pipes 42 and 44 include a liquid connecting pipe 42 and a gasconnecting pipe 44.

The numbers (two each) of the heat source units 100, the utilizationunits 300, and the connection units 200 depicted in FIG. 1 are merelyexemplified and should not limit the present invention. For example,there may be provided one or at least three heat source units.Furthermore, there may be provided one or at least three (e.g. a largenumber such as ten or more) utilization units or connection units. Here,each of the utilization units is individually provided with the singleconnection unit. The present invention should not be limited to thisconfiguration, but the plurality of connection units to be describedbelow may be collected to constitute a single unit.

Each of the utilization units 300 in the present air conditioner 10 isconfigured to execute cooling operation or heating operationindependently from the remaining utilization unit 300. In other words,in the present air conditioner 10, while part of the utilization units(e.g. the utilization unit 300A) is executing cooling operation forcooling an air conditioning target space corresponding to theseutilization units, the remaining utilization unit (e.g. the utilizationunit 300B) can execute heating operation for heating an air conditioningtarget space corresponding to those utilization units. In the presentair conditioner 10, the utilization unit 300 executing heating operationsends the refrigerant to the utilization unit 300 executing coolingoperation to achieve heat recovery between the utilization units 300.The air conditioner 10 is configured to balance thermal loads of theheat source units 100 in accordance with the entire thermal loads of theutilization units 300 also in consideration of the heat recovery.

(2) Detailed Configurations

(2-1) Heat Source Unit

The heat source unit 100A will be described with reference to FIGS. 2 to4. The heat source unit 100B has a configuration being similar to theheat source unit 100A. The heat source unit 100B will not be describedherein to avoid repeated description.

FIG. 2 depicts only part of constituents in the heat source unit 100Bfor simplified depiction. The actual heat source unit 100B has aconfiguration being similar to the heat source unit 100A.

The heat source unit 100A is installed in a machine chamber (theinterior of a room) of the building provided with the air conditioner10, though not limited in terms of its installation site. The heatsource unit 100A may alternatively be disposed outdoors.

The heat source unit 100A according to the present embodiment utilizeswater as a heat source. In the heat source unit 100A, heat is exchangedbetween the refrigerant and water circulating in a water circuit (notdepicted) to heat or cool the refrigerant. The heat source of the heatsource unit 100A is not limited to water, but may alternatively be anyother heating medium (e.g. a thermal-storage medium such as brine orhydrate slurry). Examples of the heat source of the heat source unit100A may include a refrigerant. Examples of the heat source of the heatsource unit 100A may include air.

The heat source unit 100A is connected to the utilization units 300 viathe refrigerant connection pipes 32, 34, and 36, the connection units200, and the connecting pipes 42 and 44. The heat source unit 100A andthe utilization units 300 constitute a refrigerant circuit 50 (see FIG.2). The refrigerant circulates in the refrigerant circuit 50 while theair conditioner 10 is in operation.

The refrigerant adopted in the present embodiment is a substance thatabsorbs peripheral heat in a liquid state to come into a gaseous stateand radiates heat to the periphery in the gaseous state to come into theliquid state in the refrigerant circuit 50. Examples of the refrigerantinclude a fluorocarbon refrigerant, though not limited in terms of itstype.

As depicted in FIG. 2, the heat source unit 100A mainly includes a heatsource-side refrigerant circuit 50 a constituting part of therefrigerant circuit 50. The heat source-side refrigerant circuit 50 aincludes a compressor 110, a heat source-side heat exchanger 140exemplifying a main heat exchanger, and a heat source-side flow-ratecontrol valve 150. The heat source-side refrigerant circuit 50 a alsoincludes a first flow path switching mechanism 132 and a second flowpath switching mechanism 134. The heat source-side refrigerant circuit50 a further includes an oil separator 122 and an accumulator 124. Theheat source-side refrigerant circuit 50 a further includes a receiver180 and a gas vent pipe flow-rate control valve 182. The heatsource-side refrigerant circuit 50 a further includes a subcooling heatexchanger 170 and a second suction return valve 172. The heatsource-side refrigerant circuit 50 a further includes a cooling heatexchanger 160, a first suction return valve 162, and a capillary 164.The heat source-side refrigerant circuit 50 a further includes a bypassvalve 128. The heat source-side refrigerant circuit 50 a furtherincludes a liquid-side shutoff valve 22, a high and low-pressuregas-side shutoff valve 24, and a low-pressure gas-side shutoff valve 26.

The heat source unit 100A includes a casing 106, an electric componentbox 102, a fan 166, pressure sensors P1 and P2, temperature sensors T1,T2, T3, T4, and Ta, and a heat source unit controller 190 (see FIG. 2and FIG. 3). The casing 106 is a housing accommodating variousconstituent equipment of the heat source unit 100A, such as thecompressor 110 and the heat source-side heat exchanger 140.

Such various constituents of the heat source-side refrigerant circuit 50a, the electric component box 102, the fan 166, the pressure sensors P1and P2, the temperature sensors T1, T2, T3, T4, and Ta, and the heatsource unit controller 190 will be described in more detail below.

(2-1-1) Heat Source-Side Refrigerant Circuit

(2-1-1-1) Compressor

The compressor 110 is of a positive-displacement type such as a scrolltype or a rotary type, though not limited in terms of its type. Thecompressor 110 has a hermetic structure incorporating a compressor motor(not depicted). The compressor 110 is configured to vary operatingcapacity through inverter control of the compressor motor.

The compressor 110 has a suction port (not depicted) connected to asuction pipe 110 a (see FIG. 2). The compressor 110 compresses alow-pressure refrigerant sucked via the suction port, and thendischarges the compressed refrigerant from a discharge port (notdepicted). The discharge port of the compressor 110 is connected to adischarge pipe 110 b (see FIG. 2).

(2-1-1-2) Oil Separator

The oil separator 122 separates lubricant from gas discharged from thecompressor 110. The oil separator 122 is provided at the discharge pipe110 b. The lubricant separated by the oil separator 122 returns to asuction side (the suction pipe 110 a) of the compressor 110 via thecapillary 126 (see FIG. 2).

(2-1-1-3) Accumulator

The accumulator 124 is provided at the suction pipe 110 a (see FIG. 2).The accumulator 124 is a reservoir temporarily storing a low-pressurerefrigerant to be sucked into the compressor 110 and performinggas-liquid separation. In the accumulator 124, a refrigerant in agas-liquid two-phase state is separated into a gas refrigerant and aliquid refrigerant, and the compressor 110 receives mainly the gasrefrigerant.

(2-1-1-4) First Flow Path Switching Mechanism

The first flow path switching mechanism 132 is configured to switch aflow direction of a refrigerant flowing in the heat source-siderefrigerant circuit 50 a. The first flow path switching mechanism 132 isexemplarily constituted by a four-way switching valve as depicted inFIG. 2. The four-way switching valve adopted as the first flow pathswitching mechanism 132 is configured to block a flow of a refrigerantin one refrigerant flow path to substantially function as a three-wayvalve.

In a case where the heat source-side heat exchanger 140 functions as aradiator (condenser) for a refrigerant flowing in the heat source-siderefrigerant circuit 50 a (hereinafter, also called a “radiatingoperation state”), the first flow path switching mechanism 132 connectsa discharge side (the discharge pipe 110 b) of the compressor 110 and agas side of the heat source-side heat exchanger 140 (see a solid line inthe first flow path switching mechanism 132 in FIG. 2). In another casewhere the heat source-side heat exchanger 140 functions as a heatabsorber (evaporator) for a refrigerant flowing in the heat source-siderefrigerant circuit 50 a (hereinafter, also called a “heat absorbingoperation state”), the first flow path switching mechanism 132 connectsthe suction pipe 110 a and the gas side of the heat source-side heatexchanger 140 (see a broken line in the first flow path switchingmechanism 132 in FIG. 2).

(2-1-1-5) Second Flow Path Switching Mechanism

The second flow path switching mechanism 134 is configured to switch aflow direction of a refrigerant flowing in the heat source-siderefrigerant circuit 50 a. The second flow path switching mechanism 134is exemplarily constituted by a four-way switching valve as depicted inFIG. 2. The four-way switching valve adopted as the second flow pathswitching mechanism 134 is configured to block a flow of a refrigerantin one refrigerant flow path to substantially function as a three-wayvalve.

In a case where a high-pressure gas refrigerant discharged from thecompressor 110 is sent to the high and low-pressure gas-refrigerantconnection pipe 34 (hereinafter, also called a “radiation load operationstate”), the second flow path switching mechanism 134 connects thedischarge side (the discharge pipe 110 b) of the compressor 110 and thehigh and low-pressure gas-side shutoff valve 24 (see a broken line inthe second flow path switching mechanism 134 in FIG. 2). In another casewhere the high-pressure gas refrigerant discharged from the compressor110 is not sent to the high and low-pressure gas-refrigerant connectionpipe 34 (hereinafter, also called an “evaporation load operationstate”), the second flow path switching mechanism 134 connects the highand low-pressure gas-side shutoff valve 24 and the suction pipe 110 a ofthe compressor 110 (see a solid line in the second flow path switchingmechanism 134 in FIG. 2).

(2-1-1-6) Heat Source-Side Heat Exchanger

The heat source-side heat exchanger 140 exemplifying the main heatexchanger causes heat exchange between the refrigerant and the heatsource (cooling water or warm water circulating in the water circuit inthe present embodiment). Such liquid fluid is not controlled at the airconditioner 10 in terms of its temperature and its flow rate, althoughthe present invention is not limited to such a configuration. The heatsource-side heat exchanger 140 is exemplarily configured as a plate heatexchanger. The heat source-side heat exchanger 140 has the gas side forthe refrigerant connected to the first flow path switching mechanism 132via a pipe, and also has the liquid side for the refrigerant connectedto the heat source-side flow-rate control valve 150 via a pipe (see FIG.2).

(2-1-1-7) Heat Source-Side Flow-Rate Control Valve

The heat source-side flow-rate control valve 150 is configured tocontrol a flow rate of a refrigerant flowing in the heat source-sideheat exchanger 140. The heat source-side flow-rate control valve 150 isprovided at the liquid side (on a pipe connecting the heat source-sideheat exchanger 140 and the liquid-side shutoff valve 22) of the heatsource-side heat exchanger 140 (see FIG. 2). In other words, the heatsource-side flow-rate control valve 150 is provided on a pipe connectingthe heat source-side heat exchanger 140 and utilization heat exchangers310 in the utilization units 300. The heat source-side flow-rate controlvalve 150 is exemplarily configured as an electric expansion valvehaving a controllable opening degree.

(2-1-1-8) Receiver and Gas Vent Pipe Flow-Rate Control Valve

The receiver 180 is a reservoir temporarily storing a refrigerantflowing between the heat source-side heat exchanger 140 and theutilization units 300. The receiver 180 is disposed between the heatsource-side flow-rate control valve 150 and the liquid-side shutoffvalve 22, on a pipe connecting the liquid side of the heat source-sideheat exchanger 140 and the utilization units 300 (see FIG. 2). Thereceiver 180 has a top portion connected to a receiver gas vent pipe 180a (see FIG. 2). The receiver gas vent pipe 180 a connects the topportion of the receiver 180 and the suction side of the compressor 110.

The receiver gas vent pipe 180 a is provided with the gas vent pipeflow-rate control valve 182 configured to control a flow rate of arefrigerant to be subjected to gas venting from the receiver 180. Thegas vent pipe flow-rate control valve 182 is exemplarily configured asan electric expansion valve having a controllable opening degree.

(2-1-1-9) Cooling Heat Exchanger and First Suction Return Valve

The heat source-side refrigerant circuit 50 a is provided with a firstsuction return pipe 160 a branching at a branching point B1 from a pipeconnecting the receiver 180 and the liquid-side shutoff valve 22 andconnected to the suction side (the suction pipe 110 a) of the compressor110 (see FIG. 2). The first suction return pipe 160 a connects the pipeconnecting between the heat source-side heat exchanger 140 and theutilization heat exchangers 310 in the utilization units 300 and thesuction pipe 110 a of the compressor 110.

The first suction return pipe 160 a is provided with the cooling heatexchanger 160, the first suction return valve 162, and the capillary 164(see FIG. 2). The first suction return valve 162 exemplifies a valve.The cooling heat exchanger 160 is supplied with a refrigerant to coolthe interior of the casing 106 of the heat source unit 100A. The firstsuction return valve 162 switches to supply or not to supply the coolingheat exchanger 160 with a refrigerant. The capillary 164 is disposeddownstream of the first suction return valve 162 in a refrigerant flowdirection F (see FIG. 2) of the refrigerant flowing to the cooling heatexchanger 160 when the first suction return valve 162 is opened. Therefrigerant flow direction F is a direction from the branching point B1toward the suction side (the suction pipe 110 a) of the compressor 110.The capillary 164 may alternatively be disposed upstream of the firstsuction return valve 162 in the refrigerant flow direction F.

The first suction return pipe 160 a may be provided with an electricexpansion valve having a controllable opening degree, in place of thefirst suction return valve 162 and the capillary 164.

The cooling heat exchanger 160 is configured to cause heat exchangebetween a refrigerant flowing in the cooling heat exchanger 160 and air.The cooling heat exchanger 160 is exemplarily of a cross-fin type,though not limited in terms of its type. The cooling heat exchanger 160is supplied with air by the fan 166 to be described later for stimulatedheat exchange between the refrigerant and the air.

(2-1-1-10) Subcooling Heat Exchanger and Suction Return Flow-RateControl Valve

The heat source-side refrigerant circuit 50 a is provided with a secondsuction return pipe 170 a branching at a branching point B2 from thepipe connecting the receiver 180 and the liquid-side shutoff valve 22and connected to the suction side (the suction pipe 110 a) of thecompressor 110 (see FIG. 2). The second suction return pipe 170 a isprovided with the second suction return valve 172 (see FIG. 2). Thesecond suction return valve 172 is exemplarily configured as an electricexpansion valve having a controllable opening degree.

The subcooling heat exchanger 170 is provided on the pipe connecting thereceiver 180 and the liquid-side shutoff valve 22, at a position shiftedfrom the branching point B2 toward the liquid-side shutoff valve 22. Thesubcooling heat exchanger 170 causes heat exchange between therefrigerant flowing through the pipe connecting the receiver 180 and theliquid-side shutoff valve 22 and the refrigerant flowing through thesecond suction return pipe 170 a to cool the refrigerant flowing throughthe pipe connecting the receiver 180 and the liquid-side shutoff valve22. The subcooling heat exchanger 170 is exemplarily configured as adouble pipe heat exchanger.

(2-1-1-11) Bypass Valve

The bypass valve 128 is provided on a pipe connecting the oil separator122 and the suction pipe 110 a of the compressor 110 (see FIG. 2). Thebypass valve 128 is configured as an electromagnetic valve controlled toopen and close. When the bypass valve 128 is controlled to open, therefrigerant discharged from the compressor 110 partially flows into thesuction pipe 110 a.

The bypass valve 128 is appropriately controlled to open or close inaccordance with an operation situation of the air conditioner 10. In acase where the compressor motor is inverter controlled to reduce theoperating capacity of the compressor 110 and the operating capacity thusreduced is still excessive, the bypass valve 128 may be opened to reducequantity of the refrigerant circulating in the refrigerant circuit 50.The bypass valve 128 may be opened at predetermined timing to increase aheating degree at the suction side of the compressor 110 for preventionof liquid compression.

(2-1-1-12) Liquid-Side Shutoff Valve, High and Low-Pressure Gas-SideShutoff Valve, and Low-Pressure Gas-Side Shutoff Valve

The liquid-side shutoff valve 22, the high and low-pressure gas-sideshutoff valve 24, and the low-pressure gas-side shutoff valve 26 aremanually operated to open or close upon refrigerant filling, pump down,and the like.

The liquid-side shutoff valve 22 has a first end connected to theliquid-refrigerant connection pipe 32 and a second end connected to arefrigerant pipe extending toward the heat source-side flow-rate controlvalve 150 via the receiver 180 (see FIG. 2).

The high and low-pressure gas-side shutoff valve 24 has a first endconnected to the high and low-pressure gas-refrigerant connection pipe34 and a second end connected to a refrigerant pipe extending to thesecond flow path switching mechanism 134 (see FIG. 2).

The low-pressure gas-side shutoff valve 26 has a first end connected tothe low-pressure gas-refrigerant connection pipe 36 and a second endconnected to a refrigerant pipe extending to the suction pipe 110 a (seeFIG. 2).

(2-1-2) Electric Component Box and Fan

The casing 106 of the heat source unit 100A accommodates the electriccomponent box 102. The electric component box 102 has a rectangularparallelepiped shape, though not limited in terms of its shape. Theelectric component box 102 accommodates electric components 104configured to control operation of the various constituents, such as thecompressor 110, the flow path switching mechanisms 132 and 134, and thevalves 150, 182, 172, 162, and 128, in the heat source unit 100A in theair conditioner 10 (see FIG. 3). The electric components 104 includeelectric components constituting an inverter circuit for control of themotor of the compressor 110, as well as electric components such as amicrocomputer and a memory constituting the heat source unit controller190 to be described later.

The electric component box 102 has a lower opening (not depicted)allowing air to enter the electric component box 102, and an upperopening (not depicted) allowing air to blow out of the electriccomponent box 102. The fan 166 is provided adjacent to the upper opening(see FIG. 3). The fan 166 is provided, on an air blow-out side(downstream in an air blow-out direction), with the cooling heatexchanger 160 (see FIG. 3 and FIG. 4). When the fan 166 operates, airflowed into the electric component box 102 through the lower openingmoves upward in the electric component box 102 and blows out of theelectric component box 102 through the upper opening. When the air movesin the electric component box 102, the air moving in the electriccomponent box 102 cools the electric components 104. Air absorbed heatfrom the electric components 104 and thus warmed blows out of theelectric component box 102 into the casing 106 through the upperopening. The present air conditioner 10 includes the fan 166 configuredas a constant-speed fan. The fan 166 may alternatively be a variablespeed fan.

The casing 106 has a suction opening (not depicted) disposed in a lowerportion of a side surface, and an exhaust opening (not depicted)disposed in a top portion, to allow ventilation in the casing 106 withair from outside the casing 106. The interior of the casing 106 isincreased in temperature in a case where the ventilation is insufficientrelatively to heat generated by the electric components 104, the motorof the compressor 110, and the like, or in a case where the casing 106has relatively high ambient temperature.

(2-1-3) Pressure Sensor

The heat source unit 100A includes the plurality of pressure sensorsconfigured to measure pressure of a refrigerant. The pressure sensorsinclude the high pressure sensor P1 and the low pressure sensor P2.

The high pressure sensor P1 is disposed on the discharge pipe 110 b (seeFIG. 2). The high pressure sensor P1 measures pressure of a refrigerantdischarged from the compressor 110. In other words, the high pressuresensor P1 measures high pressure in the refrigeration cycle.

The low pressure sensor P2 is disposed on the suction pipe 110 a (seeFIG. 2). The low pressure sensor P2 measures pressure of a refrigerantsucked into the compressor 110. In other words, the low pressure sensorP2 measures low pressure in the refrigeration cycle.

(2-1-4) Temperature Sensor

The heat source unit 100A includes the plurality of temperature sensorsconfigured to measure temperature of a refrigerant.

The temperature sensors configured to measure temperature of arefrigerant may include the liquid-refrigerant temperature sensor T1provided on the pipe connecting the receiver 180 and the liquid-sideshutoff valve 22, at a position shifted from the branching point B1,where the first suction return pipe 160 a branches, toward the receiver180 (see FIG. 2). The temperature sensors configured to measuretemperature of a refrigerant may also include the sucked refrigeranttemperature sensor T2 provided upstream of the accumulator 124, on thesuction pipe 110 a (see FIG. 2). The temperature sensors configured tomeasure temperature of a refrigerant also include the gas-sidetemperature sensor T3 provided on the gas side of the heat source-sideheat exchanger 140, and the liquid-side temperature sensor T4 providedon the liquid side of the heat source-side heat exchanger 140 (see FIG.2). The temperature sensors configured to measure temperature of arefrigerant may also include a discharge temperature sensor (notdepicted) provided on the discharge pipe 110 b of the compressor 110.The temperature sensors configured to measure temperature of arefrigerant may also include temperature sensors (not depicted) providedupstream and downstream of the subcooling heat exchanger 170 in arefrigerant flow direction of the second suction return pipe 170 a. Thetemperature sensors configured to measure temperature of a refrigerantmay also include a temperature sensor provided downstream of the coolingheat exchanger 160 in a refrigerant flow direction of the first suctionreturn pipe 160 a.

The heat source unit 100A includes the casing internal temperaturesensor Ta configured to measure temperature in the casing 106. Thecasing internal temperature sensor Ta is installed adjacent to a ceilingof the casing 106, though not limited in terms of its installation site(see FIG. 3).

(2-1-5) Heat Source Unit Controller

The heat source unit controller 190 includes the microcomputer and thememory provided for control of the heat source unit 100A. The heatsource unit controller 190 is electrically connected to the varioussensors including the pressure sensors P1 and P2 and the temperaturesensors T1, T2, T3, T4, and Ta. FIG. 2 omits depicting connectionsbetween the heat source unit controller 190 and the sensors. The heatsource unit controller 190 is also electrically connected to connectionunit controllers 290 in the connection units 200A and 200B, andutilization unit controllers 390 in the utilization units 300A and 300B,for transmission and reception of control signals to and from theconnection unit controllers 290 and the utilization unit controllers390. The heat source unit controllers 190, the connection unitcontrollers 290, and the utilization unit controllers 390 operate incooperation as a control unit 400 configured to control the airconditioner 10. Control of the air conditioner 10 by the control unit400 will be described later.

(2-2) Utilization Unit

The utilization unit 300A will be described with reference to FIG. 2.The utilization unit 300B is configured similarly to the utilizationunit 300A and thus will not be described herein to avoid repeateddescription.

The utilization unit 300A may be of a ceiling embedded type and beembedded in a ceiling of the room in the building as exemplarilydepicted in FIG. 1. The utilization unit 300A should not be limited tothe ceiling embedded type, but may alternatively be of a ceiling pendanttype, a wall mounted type to be mounted on a wall surface in the room,or the like. The utilization unit 300A and the utilization unit 300B maynot be of a same type.

The utilization unit 300A is connected to the heat source units 100 viathe connecting pipes 42 and 44, the connection unit 200A, and therefrigerant connection pipes 32, 34, and 36. The utilization unit 300Aand the heat source unit 100 constitute the refrigerant circuit 50.

The utilization unit 300A includes a utilization refrigerant circuit 50b constituting part of the refrigerant circuit 50. The utilizationrefrigerant circuit 50 b mainly includes a utilization flow-rate controlvalve 320 and the utilization heat exchanger 310. The utilization unit300A further includes temperature sensors T5 a and T6 a, and theutilization unit controller 390. The utilization unit 300B includestemperature sensors denoted by reference signs T5 b and T6 b in FIG. 2for convenience of description, but the temperature sensors T5 b and T6b are configured similarly to the temperature sensors T5 a and T6 aincluded in the utilization unit 300A.

(2-2-1) Utilization Refrigerant Circuit

(2-2-1-1) Utilization Flow-Rate Control Valve

The utilization flow-rate control valve 320 is configured to control aflow rate of a refrigerant flowing in the utilization heat exchanger310. The utilization flow-rate control valve 320 is provided on a liquidside of the utilization heat exchanger 310 (see FIG. 2). The utilizationflow-rate control valve 320 is exemplarily configured as an electricexpansion valve having a controllable opening degree.

(2-2-1-2) Utilization Heat Exchanger

The utilization heat exchanger 310 causes heat exchange between arefrigerant and indoor air. Examples of the utilization heat exchanger310 include a fin-and-tube heat exchanger constituted by a plurality ofheat transfer tubes and a fin. The utilization unit 300A includes anindoor fan (not depicted) configured to suck indoor air into theutilization unit 300A, supply the utilization heat exchanger 310 withthe indoor air, and supply air after heat exchange in the utilizationheat exchanger 310 into the room. The indoor fan is driven by an indoorfan motor (not depicted).

(2-2-2) Temperature Sensor

The utilization unit 300A includes the plurality of temperature sensorsconfigured to measure temperature of a refrigerant. The temperaturesensors configured to measure temperature of a refrigerant include theliquid-side temperature sensor T5 a configured to measure temperature ofthe refrigerant on the liquid side (at an outlet of the utilization heatexchanger 310 functioning as a radiator for a refrigerant) of theutilization heat exchanger 310. The temperature sensors configured tomeasure temperature of a refrigerant also include the gas-sidetemperature sensor T6 a configured to measure temperature of therefrigerant on a gas side (at an inlet of the utilization heat exchanger310 functioning as a radiator for a refrigerant) of the utilization heatexchanger 310.

The utilization unit 300A includes a temperature sensor (not depicted)configured to measure temperature in the room as the air conditioningtarget space.

(2-2-3) Utilization Unit Controller

The utilization unit controller 390 in the utilization unit 300Aincludes a microcomputer and a memory provided for control of theutilization unit 300A. The utilization unit controller 390 in theutilization unit 300A is electrically connected to various sensorsincluding the temperature sensors T5 a and T6 a (FIG. 2 does not depictconnection between the utilization unit controller 390 and the sensors).The utilization unit controller 390 in the utilization unit 300A is alsoelectrically connected to the heat source unit controller 190 in theheat source unit 100A and the connection unit controller 290 in theconnection unit 200A, for transmission and reception of control signalsto and from the heat source unit controller 190 and the connection unitcontroller 290. The heat source unit controllers 190, the connectionunit controllers 290, and the utilization unit controllers 390 operatein cooperation as the control unit 400 configured to control the airconditioner 10. Control of the air conditioner 10 by the control unit400 will be described later.

(2-3) Connection Unit

The connection unit 200A will be described with reference to FIG. 2. Theconnection unit 200B is configured similarly to the connection unit200A, and thus will not be described herein to avoid repeateddescription.

The connection unit 200A and the utilization unit 300A are installedtogether. The connection unit 200A may be installed in a ceiling cavityof the room and adjacent to the utilization unit 300A.

The connection unit 200A is connected to the heat source units 100 (100Aand 100B) via the refrigerant connection pipes 32, 34, and 36. Theconnection unit 200A is also connected to the utilization unit 300A viathe connecting pipes 42 and 44. The connection unit 200A constitutespart of the refrigerant circuit 50. The connection unit 200A is disposedbetween the heat source unit 100 and the utilization unit 300A, andswitches a flow of a refrigerant flowing into the heat source unit 100and the utilization unit 300A.

The connection unit 200A includes a connection refrigerant circuit 50 cconstituting part of the refrigerant circuit 50. The connectionrefrigerant circuit 50 c mainly includes a liquid refrigerant pipe 250and a gas refrigerant pipe 260. The connection unit 200A furtherincludes the connection unit controller 290.

(2-3-1) Connection Refrigerant Circuit

(2-3-1-1) Liquid Refrigerant Pipe

The liquid refrigerant pipe 250 includes a main liquid refrigerant pipe252 and a branching liquid refrigerant pipe 254.

The main liquid refrigerant pipe 252 connects the liquid-refrigerantconnection pipe 32 and the liquid connecting pipe 42. The branchingliquid refrigerant pipe 254 connects the main liquid refrigerant pipe252 and a low-pressure gas refrigerant pipe 264 of the gas refrigerantpipe 260 to be described later. The branching liquid refrigerant pipe254 is provided with a branching pipe control valve 220. The branchingpipe control valve 220 is exemplarily configured as an electricexpansion valve having a controllable opening degree. The main liquidrefrigerant pipe 252 is provided with a subcooling heat exchanger 210disposed at a position shifted from a branching point of the branchingliquid refrigerant pipe 254 toward the liquid connecting pipe 42. If thebranching pipe control valve 220 is opened when the refrigerant flowsfrom the liquid side to the gas side in the utilization heat exchanger310 of the utilization unit 300A, the subcooling heat exchanger 210causes heat exchange between the refrigerant flowing through the mainliquid refrigerant pipe 252 and the refrigerant flowing through thebranching liquid refrigerant pipe 254 from the main liquid refrigerantpipe 252 to the low-pressure gas refrigerant pipe 264 to cool therefrigerant flowing through the main liquid refrigerant pipe 252. Thesubcooling heat exchanger 210 is exemplarily configured as a double pipeheat exchanger.

(2-3-1-2) Gas Refrigerant Pipe

The gas refrigerant pipe 260 includes a high and low-pressure gasrefrigerant pipe 262, the low-pressure gas refrigerant pipe 264, and ajoined gas refrigerant pipe 266. The high and low-pressure gasrefrigerant pipe 262 has a first end connected to the high andlow-pressure gas-refrigerant connection pipe 34 and a second endconnected to the joined gas refrigerant pipe 266. The low-pressure gasrefrigerant pipe 264 has a first end connected to the low-pressuregas-refrigerant connection pipe 36 and a second end connected to thejoined gas refrigerant pipe 266. The joined gas refrigerant pipe 266 hasa first end connected to the high and low-pressure gas refrigerant pipe262 and the low-pressure gas refrigerant pipe 264, and a second endconnected to the gas connecting pipe 44. The high and low-pressure gasrefrigerant pipe 262 is provided with a high and low-pressure valve 230.The low-pressure gas refrigerant pipe 264 is provided with a lowpressure valve 240. Each of the high and low-pressure valve 230 and thelow pressure valve 240 may be configured as a motor valve.

(2-3-2) Connection Unit Controller

The connection unit controller 290 includes a microcomputer and a memoryprovided for control of the connection unit 200A. The connection unitcontroller 290 is electrically connected to the heat source unitcontroller 190 in the heat source unit 100A and the utilization unitcontroller 390 in the utilization unit 300A, for transmission andreception of control signals to and from the heat source unit controller190 and the utilization unit controller 390. The heat source unitcontrollers 190, the connection unit controllers 290, and theutilization unit controllers 390 operate in cooperation as the controlunit 400 configured to control the air conditioner 10. Control of theair conditioner 10 by the control unit 400 will be described later.

(2-3-3) Refrigerant Flow Rate Switching by Connection Unit

When the utilization unit 300A executes cooling operation, theconnection unit 200A brings the low pressure valve 240 into an openedstate, and sends the refrigerant flowing from the liquid-refrigerantconnection pipe 32 into the main liquid refrigerant pipe 252 to theutilization heat exchanger 310 via the liquid connecting pipe 42 and theutilization flow-rate control valve 320 of the utilization refrigerantcircuit 50 b in the utilization unit 300A. The connection unit 200Asends, to the low-pressure gas-refrigerant connection pipe 36 via thejoined gas refrigerant pipe 266 and the low-pressure gas refrigerantpipe 264, the refrigerant evaporated through heat exchange with indoorair in the utilization heat exchanger 310 of the utilization unit 300Aand flowed into the gas connecting pipe 44.

When the utilization unit 300A executes heating operation, theconnection unit 200A brings the low pressure valve 240 into a closedstate and brings the high and low-pressure valve 230 into the openedstate, and sends the refrigerant flowing through the high andlow-pressure gas-refrigerant connection pipe 34 into the high andlow-pressure gas refrigerant pipe 262, to the utilization heat exchanger310 in the utilization refrigerant circuit 50 b of the utilization unit300A via the joined gas refrigerant pipe 266 and gas connecting pipe 44.The connection unit 200A sends, to the liquid-refrigerant connectionpipe 32 via the main liquid refrigerant pipe 252, the refrigerant whichradiated heat through heat exchange with indoor air in the utilizationheat exchanger 310 and flowed into the liquid connecting pipe 42 via theutilization flow-rate control valve 320.

(2-4) Control Unit

The control unit 400 is a functional unit configured to control the airconditioner 10. To function as the control unit 400, the heat sourceunit controllers 190 in the heat source units 100, the connection unitcontrollers 290 in the connection units 200, and the utilization unitcontrollers 390 in the utilization units 300 operate in cooperation. Thepresent embodiment is not limited to this configuration, but the controlunit 400 may alternatively be configured as a control device independentfrom the heat source units 100, the connection units 200, and theutilization units 300.

The control unit 400 causes a microcomputer included in the control unit400 to execute a program stored in a memory included in the control unit400 to control operation of the air conditioner 10. Herein, the memoriesof the heat source unit controllers 190, the connection unit controllers290, and the utilization unit controllers 390 are collectively calledthe memory of the control unit 400, whereas the microcomputers of theheat source unit controllers 190, the connection unit controllers 290,and the utilization unit controllers 390 are collectively called themicrocomputer of the control unit 400.

The control unit 400 controls operation of various constituent equipmentof the heat source units 100, the connection units 200, and theutilization units 300 in accordance with measurement values of varioussensors included in the air conditioner 10 as well as a command andsetting inputted by a user to an operation unit (not depicted; e.g. aremote controller) to achieve appropriate operation. The control unit400 has operation control target equipment including the compressor 110,the heat source-side flow-rate control valve 150, the first flow pathswitching mechanism 132, the second flow path switching mechanism 134,the gas vent pipe flow-rate control valve 182, the first suction returnvalve 162, the second suction return valve 172, the bypass valve 128,and the fan 166 in each of the heat source units 100. The operationcontrol target equipment of the control unit 400 further include theutilization flow-rate control valve 320 and the indoor fan in each ofthe utilization units 300. The operation control target equipment of thecontrol unit 400 also include the branching pipe control valve 220, thehigh and low-pressure valve 230, and the low pressure valve 240 in eachof the connection units 200.

Brief description will be made later to control of various constituentequipment in the air conditioner 10 by the control unit 400 duringcooling operation (when the utilization units 300A and 300B both executecooling operation), during heating operation (when the utilization units300A and 300B both execute heating operation), and during simultaneouscooling and heating operation (when the utilization unit 300A executescooling operation and the utilization unit 300B executes heatingoperation) of the air conditioner 10.

Described further below is control to open or close the first suctionreturn valve 162 (configured to switch to supply or not to supply thecooling heat exchanger 160 with a refrigerant) by the control unit 400.

The microcomputer of the control unit 400 includes, as functional unitsrelevant to control of the first suction return valve 162, a firstderiving unit 402, a second deriving unit 404, and a controller 406 asdepicted in FIG. 5.

(2-4-1) First Deriving Unit

The first deriving unit 402 derives first pressure Pr1 upstream of thefirst suction return valve 162 in the refrigerant flow direction F (seeFIG. 2) of the refrigerant flowing to the cooling heat exchanger 160when the first suction return valve 162 is opened. The refrigerant flowdirection F is a direction along the first suction return pipe 160 afrom the branching point B1 on the pipe connecting the receiver 180 andthe liquid-side shutoff valve 22 toward the suction side (the suctionpipe 110 a) of the compressor 110. The first deriving unit 402 derivespressure of the refrigerant around the branching point B1 on the pipeconnecting the receiver 180 and the liquid-side shutoff valve 22.

Specifically, the first deriving unit 402 calculates the first pressurePr1 in accordance with information on a relation between temperature andpressure of a refrigerant (e.g. a correspondence table on saturationtemperature and pressure of a refrigerant) stored in the memory of thecontrol unit 400 and temperature measured by the liquid-refrigeranttemperature sensor T1 disposed adjacent to the branching point B1 on therefrigerant pipe.

In this embodiment, the first deriving unit 402 calculates the firstpressure Pr1 in accordance with the temperature measured by theliquid-refrigerant temperature sensor T1. However, a method of derivingthe first pressure Pr1 is not limited thereto. In a case where the firstflow path switching mechanism 132 connects the discharge pipe 110 b andthe gas side of the heat source-side heat exchanger 140 to cause theheat source-side heat exchanger 140 to function as a radiator, the firstderiving unit 402 may calculate the first pressure Pr1 by subtracting,from pressure measured by the pressure sensor P1, a pressure lossbetween the pressure sensor P1 and the branching point B1 obtained froma current opening degree of the heat source-side flow-rate control valve150 or the like. There may be provided a pressure sensor adjacent to thebranching point B1 on the refrigerant pipe and the first deriving unit402 may calculate the first pressure Pr1 directly from a measurementvalue of the pressure sensor.

(2-4-2) Second Deriving Unit

The second deriving unit 404 derives second pressure Pr2 downstream ofthe cooling heat exchanger 160 in the refrigerant flow direction F (seeFIG. 2) of the refrigerant flowing to the cooling heat exchanger 160when the first suction return valve 162 is opened. In other words, thesecond deriving unit 404 derives pressure of the refrigerant in thesuction pipe 110 a.

Specifically, the second deriving unit 404 derives, as the secondpressure Pr2, suction pressure of the compressor 110 measured by thepressure sensor P2. This is an exemplary method of deriving the secondpressure Pr2 by the second deriving unit 404, and the second pressurePr2 may alternatively be derived in accordance with temperature of therefrigerant or the like.

(2-4-3) Controller

The controller 406 controls to open or close the first suction returnvalve 162.

The controller 406 basically controls to open or close the first suctionreturn valve 162 in accordance with the temperature measured by thecasing internal temperature sensor Ta. Specifically, the controller 406opens the first suction return valve 162 to cool the interior of thecasing 106 when the temperature measured by the casing internaltemperature sensor Ta exceeds predetermined set temperature. When thefirst suction return valve 162 is opened, the liquid refrigerant flowsfrom the pipe connecting the receiver 180 and the liquid-side shutoffvalve 22 into the cooling heat exchanger 160. The liquid refrigerantflowed into the cooling heat exchanger 160 exchanges heat with air inthe casing 106 to cool the air and evaporates.

The controller 406 assesses, before the first suction return valve 162is actually opened to supply the cooling heat exchanger 160 with therefrigerant, whether or not the refrigerant flowing from the coolingheat exchanger 160 toward the compressor 110 comes into a wet state whenthe refrigerant is supplied to the cooling heat exchanger 160, anddetermines whether or not to open the first suction return valve 162 inaccordance with an assessment result. Specifically, the controller 406assesses whether or not the liquid refrigerant supplied to the coolingheat exchanger 160 entirely evaporates when the refrigerant is suppliedto the cooling heat exchanger 160, and determines whether or not to openthe first suction return valve 162 in accordance with an assessmentresult. In other words, the controller 406 assesses whether or not therefrigerant immediately after flowing out of the cooling heat exchanger160 entirely comes into the gaseous state when the refrigerant issupplied to the cooling heat exchanger 160, and determines whether ornot to open the first suction return valve 162 in accordance with anassessment result.

The controller 406 determines whether or not to open the first suctionreturn valve 162 in accordance with pressure difference ΔP between thefirst pressure Pr1 derived by the first deriving unit 402 and the secondpressure Pr2 derived by the second deriving unit 404. In other words,the controller 406 assesses whether or not the refrigerant flowing fromthe cooling heat exchanger 160 toward the compressor 110 comes into thewet state when the refrigerant is supplied to the cooling heat exchanger160, and determines whether or not to open the first suction returnvalve 162 in accordance with an assessment result. The controller 406also determines whether or not to open the first suction return valve162 in accordance with the assessment result, based on the temperaturemeasured by the casing internal temperature sensor Ta. In other words,the controller 406 assesses whether or not the refrigerant flowing fromthe cooling heat exchanger 160 toward the compressor 110 comes into thewet state when the refrigerant is supplied to the cooling heat exchanger160, and determines whether or not to open the first suction returnvalve 162 in accordance with an assessment result.

Specifically, the controller 406 assesses whether or not the refrigerantimmediately after flowing out of the cooling heat exchanger 160 entirelycomes into the gaseous state in the following manner when therefrigerant is supplied to the cooling heat exchanger 160.

The controller 406 calculates the pressure difference ΔP (=Pr1−Pr2)between the current first pressure Pr1 derived by the first derivingunit 402 and the current second pressure Pr2 derived by the secondderiving unit 404 before the first suction return valve 162 is opened tosupply the cooling heat exchanger 160 with the refrigerant. Thecontroller 406 then calculates a flow rate of the refrigerant expectedto be supplied to the cooling heat exchanger 160 when the first suctionreturn valve 162 is opened, in accordance with the pressure differenceΔP and information on a relation between pressure difference and a flowrate of a liquid refrigerant stored in the memory of the control unit400. Examples of the information on the relation between the pressuredifference and the flow rate of the liquid refrigerant stored in thememory of the control unit 400 include a preliminarily derived tableindicating a relation between pressure difference and a flow rate, and arelational expression between the pressure difference and the flow rate.

Further, the controller 406 calculates, before the first suction returnvalve 162 is opened to supply the cooling heat exchanger 160 with therefrigerant, quantity of the liquid refrigerant evaporable in thecooling heat exchanger 160 when the refrigerant is supplied to thecooling heat exchanger 160 in accordance with the temperature in thecasing 106 measured by the casing internal temperature sensor Ta. Morespecifically, the controller 406 calculates a flow rate of the liquidrefrigerant evaporable in the cooling heat exchanger 160 when therefrigerant is supplied to the cooling heat exchanger 160, in accordancewith the temperature in the casing 106 measured by the casing internaltemperature sensor Ta and the evaporation temperature in therefrigeration cycle. The controller 406 calculates quantity of theliquid refrigerant evaporable in the cooling heat exchanger 160 when therefrigerant is supplied to the cooling heat exchanger 160, from theevaporation temperature in the refrigeration cycle and the temperaturein the casing 106 measured by the casing internal temperature sensor Ta,in accordance with a relation between the quantity of the liquidrefrigerant evaporable in the cooling heat exchanger 160 and airtemperature in the casing 106 at different evaporation temperaturelevels in the refrigeration cycle as indicated in FIG. 6 and stored inthe memory of the control unit 400. The controller 406 calculates theevaporation temperature in the refrigeration cycle in accordance withthe second pressure Pr2 measured by the pressure sensor P2 and theinformation on the relation between temperature and pressure of arefrigerant (e.g. the correspondence table on saturation temperature andpressure of the refrigerant) stored in the memory of the control unit400. FIG. 6 conceptually indicates the relation between the quantity ofthe refrigerant evaporable in the cooling heat exchanger 160 and the airtemperature in the casing 106 at the different evaporation temperaturelevels in the refrigeration cycle, and the memory of the control unit400 may actually store information in the form of a table or amathematical expression.

The controller 406 compares quantity (hereinafter called quantity A1) ofthe liquid refrigerant evaporable in the cooling heat exchanger 160 whenthe first suction return valve 162 is opened and quantity (hereinaftercalled quantity A2) of the liquid refrigerant expected to be supplied tothe cooling heat exchanger 160 when the first suction return valve 162is opened. In a case where the quantity A2≤the quantity A1 isestablished, the controller 406 assesses that the refrigerantimmediately after flowing out of the cooling heat exchanger 160 entirelycomes into the gaseous state when the refrigerant is supplied to thecooling heat exchanger 160. The controller 406 then determines to openthe first suction return valve 162. In another case where the quantityA2>the quantity A1 is established, the controller 406 assesses that therefrigerant immediately after flowing out of the cooling heat exchanger160 is partially in the liquid state when the refrigerant is supplied tothe cooling heat exchanger 160. The controller 406 then determines notto open the first suction return valve 162 (to keep the first suctionreturn valve 162 closed).

(3) Operation of Air Conditioner

Described below is operation of the air conditioner 10 when theutilization units 300A and 300B both execute cooling operation, when theutilization units 300A and 300B both execute heating operation, and whenthe utilization unit 300A executes cooling operation and the utilizationunit 300B executes heating operation. The following description relatesto an exemplary case where only the heat source unit 100A in the heatsource units 100 operates.

Operation of the air conditioner 10 will be exemplified herein, and maybe appropriately modified within a range in which the utilization units300A and 300B can exhibit desired cooling and heating functions.

(3-1) When All Operated Utilization Units Execute Cooling Operation

The following description relates to the case where the utilizationunits 300A and 300B both execute cooling operation, in other words,where the utilization heat exchangers 310 in the utilization units 300Aand 300B each function as a heat absorber (evaporator) for a refrigerantand the heat source-side heat exchanger 140 functions as a radiator(condenser) for a refrigerant.

The control unit 400 switches the first flow path switching mechanism132 into the radiating operation state (the state indicated by the solidline of the first flow path switching mechanism 132 in FIG. 2) to causethe heat source-side heat exchanger 140 to function as a radiator for arefrigerant. The control unit 400 switches the second flow pathswitching mechanism 134 into the evaporation load operation state (thestate indicated by the solid line of the second flow path switchingmechanism 134 in FIG. 2). The control unit 400 appropriately controlsthe opening degrees of the heat source-side flow-rate control valve 150and the second suction return valve 172. The control unit 400 furthercontrols to bring the gas vent pipe flow-rate control valve 182 into afully closed state. The control unit 400 brings the branching pipecontrol valves 220 into the closed state and brings the high andlow-pressure valves 230 and the low pressure valves 240 into the openedstate in the connection units 200A and 200B, to cause the utilizationheat exchangers 310 in the utilization units 300A and 300B to eachfunction as an evaporator for a refrigerant. When the control unit 400brings the high and low-pressure valves 230 and the low pressure valves240 into the opened state, the utilization heat exchangers 310 in theutilization units 300A and 300B and the suction side of the compressor110 in the heat source unit 100A are connected via the high andlow-pressure gas-refrigerant connection pipe 34 and the low-pressuregas-refrigerant connection pipe 36. The control unit 400 appropriatelycontrols the opening degrees of the utilization flow-rate control valves320 in the utilization units 300A and 300B.

The control unit 400 operates the respective units in the airconditioner 10 as described above to allow the refrigerant to circulatein the refrigerant circuit 50 as indicated by arrows in FIG. 7A.

The high-pressure gas refrigerant compressed by and discharged from thecompressor 110 is sent to the heat source-side heat exchanger 140 viathe first flow path switching mechanism 132. The high-pressure gasrefrigerant sent to the heat source-side heat exchanger 140 radiatesheat to be condensed through heat exchange with water as the heat sourcein the heat source-side heat exchanger 140. The refrigerant whichradiated heat in the heat source-side heat exchanger 140 is flow-ratecontrolled by the heat source-side flow-rate control valve 150 and isthen sent to the receiver 180. The refrigerant sent to the receiver 180is temporarily stored in the receiver 180 and then flows out, and therefrigerant partially flows to the second suction return pipe 170 a viathe branching point B2 whereas the remaining thereof flows toward theliquid-refrigerant connection pipe 32. The refrigerant flowing from thereceiver 180 to the liquid-refrigerant connection pipe 32 is cooledthrough heat exchange in the subcooling heat exchanger 170 with therefrigerant flowing through the second suction return pipe 170 a towardthe suction pipe 110 a of the compressor 110, and then flows through theliquid-side shutoff valve 22 into the liquid-refrigerant connection pipe32. The refrigerant sent to the liquid-refrigerant connection pipe 32 isbranched into two ways to be sent to the main liquid refrigerant pipes252 in the connection units 200A and 200B. The refrigerant sent to themain liquid refrigerant pipes 252 in the connection units 200A and 200Bflows through the liquid connecting pipes 42 to be sent to theutilization flow-rate control valves 320 in the utilization units 300Aand 300B. The refrigerant sent to each of the utilization flow-ratecontrol valves 320 is flow-rate controlled by the utilization flow-ratecontrol valve 320 and is then evaporated to become a low-pressure gasrefrigerant through heat exchange in the utilization heat exchanger 310with indoor air supplied from the indoor fan (not depicted). Meanwhile,the indoor air is cooled and is supplied into the room. The low-pressuregas refrigerant flowing out of the utilization heat exchangers 310 inthe utilization units 300A and 300B is sent to the joined gasrefrigerant pipes 266 in the connection units 200A and 200B. Thelow-pressure gas refrigerant sent to each of the joined gas refrigerantpipes 266 is sent to the high and low-pressure gas-refrigerantconnection pipe 34 via the high and low-pressure gas refrigerant pipe262 as well as to the low-pressure gas-refrigerant connection pipe 36via the low-pressure gas refrigerant pipe 264. The low-pressure gasrefrigerant sent to the high and low-pressure gas-refrigerant connectionpipe 34 returns to the suction side (the suction pipe 110 a) of thecompressor 110 via the high and low-pressure gas-side shutoff valve 24and the second flow path switching mechanism 134. The low-pressure gasrefrigerant sent to the low-pressure gas-refrigerant connection pipe 36returns to the suction side (the suction pipe 110 a) of the compressor110 via the low-pressure gas-side shutoff valve 26.

(3-2) When All Operated Utilization Units Execute Heating Operation

The following description relates to the case where the utilizationunits 300A and 300B both execute heating operation, in other words,where the utilization heat exchangers 310 in the utilization units 300Aand 300B each function as a radiator (condenser) for a refrigerant andthe heat source-side heat exchanger 140 functions as a heat absorber(evaporator) for a refrigerant.

The control unit 400 switches the first flow path switching mechanism132 into an evaporating operation state (a state indicated by the brokenline of the first flow path switching mechanism 132 in FIG. 2) to causethe heat source-side heat exchanger 140 to function as a heat absorber(evaporator) for a refrigerant. The control unit 400 further switchesthe second flow path switching mechanism 134 into the radiation loadoperation state (the state indicated by the broken line of the secondflow path switching mechanism 134 in FIG. 2). The control unit 400appropriately controls the opening degree of the heat source-sideflow-rate control valve 150. The control unit 400 brings the branchingpipe control valves 220 and the low pressure valves 240 into the closedstate and brings the high and low-pressure valves 230 into the openedstate in the connection units 200A and 200B, to cause the utilizationheat exchangers 310 in the utilization units 300A and 300B to eachfunction as a radiator (condenser) for a refrigerant. When the controlunit 400 brings the high and low-pressure valves 230 into the openedstate, the discharge side of the compressor 110 and the utilization heatexchangers 310 in the utilization units 300A and 300B are connected viathe high and low-pressure gas-refrigerant connection pipe 34. Thecontrol unit 400 appropriately controls the opening degrees of theutilization flow-rate control valves 320 in the utilization units 300Aand 300B.

The control unit 400 operates the respective units in the airconditioner 10 as described above to allow the refrigerant to circulatein the refrigerant circuit 50 as indicated by arrows in FIG. 7B.

The high-pressure gas refrigerant compressed by and discharged from thecompressor 110 is sent to the high and low-pressure gas-refrigerantconnection pipe 34 via the second flow path switching mechanism 134 andthe high and low-pressure gas-side shutoff valve 24. The high-pressuregas refrigerant sent to the high and low-pressure gas-refrigerantconnection pipe 34 branches to flow into the high and low-pressure gasrefrigerant pipes 262 in the connection units 200A and 200B. Thehigh-pressure gas refrigerant flowed into the high and low-pressure gasrefrigerant pipes 262 is sent to the utilization heat exchanger 310 ineach of the utilization units 300A and 300B via the high andlow-pressure valve 230, the joined gas refrigerant pipe 266, and the gasconnecting pipe 44. The high-pressure gas refrigerant sent to theutilization heat exchanger 310 radiates heat to be condensed throughheat exchange with indoor air supplied from the indoor fan in theutilization heat exchanger 310. Meanwhile, the indoor air is heated andis supplied into the room. The refrigerant which radiated heat in theutilization heat exchangers 310 in the utilization units 300A and 300Bis flow-rate controlled by the utilization flow-rate control valves 320in the utilization units 300A and 300B and is then sent to the mainliquid refrigerant pipes 252 in the connection units 200A and 200B viathe liquid connecting pipes 42. The refrigerant sent to the main liquidrefrigerant pipes 252 is sent to the liquid-refrigerant connection pipe32 and is then sent to the receiver 180 through the liquid-side shutoffvalve 22. The refrigerant sent to the receiver 180 is temporarily storedin the receiver 180 and then flows out to be sent to the heatsource-side flow-rate control valve 150. The refrigerant sent to theheat source-side flow-rate control valve 150 is evaporated to become alow-pressure gas refrigerant through heat exchange with water as theheat source in the heat source-side heat exchanger 140 and is sent tothe first flow path switching mechanism 132. The low-pressure gasrefrigerant sent to the first flow path switching mechanism 132 thenreturns to the suction side (the suction pipe 110 a) of the compressor110.

(3-3) When Simultaneous Cooling and Heating Operation is Executed

(a) Mainly with Evaporation Load

Described below is operation of the air conditioner 10 duringsimultaneous cooling and heating operation with a superior evaporationload of the utilization units 300. A superior evaporation load in theutilization units 300 is caused, for example, in a case where a largenumber of utilization units mostly execute cooling operation and theremaining small number of the utilization units execute heatingoperation. The following description relates to an exemplary case wherethere are provided only two utilization units 300 and the utilizationunit 300A including the utilization heat exchanger 310 functioning as anevaporator for a refrigerant has a cooling load larger than a heatingload of the utilization unit 300B including the utilization heatexchanger 310 functioning as a radiator for a refrigerant.

In this case, the control unit 400 switches the first flow pathswitching mechanism 132 into the radiating operation state (the stateindicated by the solid line of the first flow path switching mechanism132 in FIG. 2) to cause the heat source-side heat exchanger 140 tofunction as a radiator for a refrigerant. The control unit 400 furtherswitches the second flow path switching mechanism 134 into the radiationload operation state (the state indicated by the broken line of thesecond flow path switching mechanism 134 in FIG. 2). The control unit400 appropriately controls the opening degrees of the heat source-sideflow-rate control valve 150 and the second suction return valve 172. Thecontrol unit 400 further controls to bring the gas vent pipe flow-ratecontrol valve 182 into a fully closed state. The control unit 400 bringsthe branching pipe control valve 220 and the high and low-pressure valve230 into the closed state and brings the low pressure valve 240 into theopened state in the connection unit 200A, to cause the utilization heatexchanger 310 in the utilization unit 300A to function as an evaporatorfor a refrigerant. The control unit 400 brings the branching pipecontrol valve 220 and the low pressure valve 240 into the closed stateand brings the high and low-pressure valve 230 into the opened state inthe connection unit 200B, to cause the utilization heat exchanger 310 inthe utilization unit 300B to function as a radiator for a refrigerant.When the valves are controlled as described above in the connection unit200A, the utilization heat exchanger 310 in the utilization unit 300Aand the suction side of the compressor 110 in the heat source unit 100Aare connected via the low-pressure gas-refrigerant connection pipe 36.When the valves are controlled as described above in the connection unit200B, the discharge side of the compressor 110 in the heat source unit100A and the utilization heat exchanger 310 in the utilization unit 300Bare connected via the high and low-pressure gas-refrigerant connectionpipe 34. The control unit 400 appropriately controls the opening degreesof the utilization flow-rate control valves 320 in the utilization units300A and 300B.

The control unit 400 operates the respective units in the airconditioner 10 as described above to allow the refrigerant to circulatein the refrigerant circuit 50 as indicated by arrows in FIG. 7C.

The high-pressure gas refrigerant compressed by and discharged from thecompressor 110 is partially sent to the high and low-pressuregas-refrigerant connection pipe 34 via the second flow path switchingmechanism 134 and the high and low-pressure gas-side shutoff valve 24,and the remaining thereof is sent to the heat source-side heat exchanger140 via the first flow path switching mechanism 132.

The high-pressure gas refrigerant sent to the high and low-pressuregas-refrigerant connection pipe 34 is sent to the high and low-pressuregas refrigerant pipe 262 in the connection unit 200B. The high-pressuregas refrigerant sent to the high and low-pressure gas refrigerant pipe262 is sent to the utilization heat exchanger 310 in the utilizationunit 300B via the high and low-pressure valve 230 and the joined gasrefrigerant pipe 266. The high-pressure gas refrigerant sent to theutilization heat exchanger 310 in the utilization unit 300B radiatesheat to be condensed through heat exchange with indoor air supplied fromthe indoor fan in the utilization heat exchanger 310. Meanwhile, theindoor air is heated and is supplied into the room. The refrigerantwhich radiated heat in the utilization heat exchanger 310 in theutilization unit 300B is flow-rate controlled by the utilizationflow-rate control valve 320 in the utilization unit 300B and is thensent to the main liquid refrigerant pipe 252 in the connection unit200B. The refrigerant sent to the main liquid refrigerant pipe 252 inthe connection unit 200B is sent to the liquid-refrigerant connectionpipe 32.

The high-pressure gas refrigerant sent to the heat source-side heatexchanger 140 radiates heat to be condensed through heat exchange withwater as the heat source in the heat source-side heat exchanger 140. Therefrigerant which radiated heat in the heat source-side heat exchanger140 is flow-rate controlled by the heat source-side flow-rate controlvalve 150 and is then sent to the receiver 180. The refrigerant sent tothe receiver 180 is temporarily stored in the receiver 180 and thenflows out, and the refrigerant partially flows to the second suctionreturn pipe 170 a via the branching point B2 whereas the remainingthereof flows toward the liquid-refrigerant connection pipe 32. Therefrigerant flowing from the receiver 180 to the liquid-refrigerantconnection pipe 32 is cooled through heat exchange in the subcoolingheat exchanger 170 with the refrigerant flowing through the secondsuction return pipe 170 a toward the suction pipe 110 a of thecompressor 110, and then flows through the liquid-side shutoff valve 22into the liquid-refrigerant connection pipe 32. The refrigerant flowinginto the liquid-refrigerant connection pipe 32 via the liquid-sideshutoff valve 22 joins the refrigerant flowing from the main liquidrefrigerant pipe 252 in the connection unit 200B.

The refrigerant in the liquid-refrigerant connection pipe 32 is sent tothe main liquid refrigerant pipe 252 in the connection unit 200A. Therefrigerant sent to the main liquid refrigerant pipe 252 in theconnection unit 200A is sent to the utilization flow-rate control valve320 in the utilization unit 300A. The refrigerant sent to theutilization flow-rate control valve 320 in the utilization unit 300A isflow-rate controlled by the utilization flow-rate control valve 320 andis then evaporated to become a low-pressure gas refrigerant through heatexchange with indoor air supplied from the indoor fan in the utilizationheat exchanger 310 of the utilization unit 300A. Meanwhile, the indoorair is cooled and is supplied into the room. The low-pressure gasrefrigerant flowing out of the utilization heat exchanger 310 in theutilization unit 300A is sent to the joined gas refrigerant pipe 266 inthe connection unit 200A. The low-pressure gas refrigerant sent to thejoined gas refrigerant pipe 266 in the connection unit 200A is sent tothe low-pressure gas-refrigerant connection pipe 36 via the low-pressuregas refrigerant pipe 264 in the connection unit 200A. The low-pressuregas refrigerant sent to the low-pressure gas-refrigerant connection pipe36 returns to the suction side (the suction pipe 110 a) of thecompressor 110 via the low-pressure gas-side shutoff valve 26.

(b) Mainly with Radiation Load

Described below is operation of the air conditioner 10 duringsimultaneous cooling and heating operation with a superior radiationload of the utilization units 300. The utilization units 300 have asuperior radiation load in an exemplary case where a large number ofutilization units mostly execute heating operation and the remainingsmall number of the utilization units execute cooling operation. Thefollowing description relates to an exemplary case where there areprovided only two utilization units 300 and the utilization unit 300Bincluding the utilization heat exchanger 310 functioning as a radiatorfor a refrigerant has a heating load larger than a cooling load of theutilization unit 300A including the utilization heat exchanger 310functioning as an evaporator for a refrigerant.

In this case, the control unit 400 switches the first flow pathswitching mechanism 132 into the evaporating operation state (the stateindicated by the broken line of the first flow path switching mechanism132 in FIG. 2) to cause the heat source-side heat exchanger 140 tofunction as an evaporator for a refrigerant. The control unit 400further switches the second flow path switching mechanism 134 into theradiation load operation state (the state indicated by the broken lineof the second flow path switching mechanism 134 in FIG. 2). The controlunit 400 appropriately controls the opening degree of the heatsource-side flow-rate control valve 150. The control unit 400 brings thehigh and low-pressure valve 230 into the closed state and brings the lowpressure valve 240 into the opened state in the connection unit 200A, tocause the utilization heat exchanger 310 in the utilization unit 300A tofunction as an evaporator for a refrigerant. The control unit 400appropriately controls the opening degree of the branching pipe controlvalve 220 in the connection unit 200A. The control unit 400 brings thebranching pipe control valve 220 and the low pressure valve 240 into theclosed state and brings the high and low-pressure valve 230 into theopened state in the connection unit 200B, to cause the utilization heatexchanger 310 in the utilization unit 300B to function as a radiator fora refrigerant. When the valves are controlled as described above in theconnection units 200A and 200B, the utilization heat exchanger 310 inthe utilization unit 300A and the suction side of the compressor 110 inthe heat source unit 100A are connected via the low-pressuregas-refrigerant connection pipe 36. When the valves are controlled asdescribed above in the connection units 200 A and 200B, the dischargeside of the compressor 110 in the heat source unit 100A and theutilization heat exchanger 310 in the utilization unit 300B areconnected via the high and low-pressure gas-refrigerant connection pipe34. The control unit 400 appropriately controls the opening degrees ofthe utilization flow-rate control valves 320 in the utilization units300A and 300B.

The control unit 400 operates the respective units in the airconditioner 10 as described above to allow the refrigerant to circulatein the refrigerant circuit 50 as indicated by arrows in FIG. 7D.

The high-pressure gas refrigerant compressed by and discharged from thecompressor 110 is sent to the high and low-pressure gas-refrigerantconnection pipe 34 via the second flow path switching mechanism 134 andthe high and low-pressure gas-side shutoff valve 24. The high-pressuregas refrigerant sent to the high and low-pressure gas-refrigerantconnection pipe 34 is sent to the high and low-pressure gas refrigerantpipe 262 in the connection unit 200B. The high-pressure gas refrigerantsent to the high and low-pressure gas refrigerant pipe 262 is sent tothe utilization heat exchanger 310 in the utilization unit 300B via thehigh and low-pressure valve 230 and the joined gas refrigerant pipe 266.The high-pressure gas refrigerant sent to the utilization heat exchanger310 in the utilization unit 300B radiates heat to be condensed throughheat exchange with indoor air supplied from the indoor fan in theutilization heat exchanger 310. Meanwhile, the indoor air is heated andis supplied into the room. The refrigerant which radiated heat in theutilization heat exchanger 310 in the utilization unit 300B is flow-ratecontrolled by the utilization flow-rate control valve 320 in theutilization unit 300B and is then sent to the main liquid refrigerantpipe 252 in the connection unit 200B. The refrigerant sent to the mainliquid refrigerant pipe 252 in the connection unit 200B is sent to theliquid-refrigerant connection pipe 32. The refrigerant in theliquid-refrigerant connection pipe 32 is partly sent to the main liquidrefrigerant pipe 252 in the connection unit 200A and the remainingthereof is sent to the receiver 180 via the liquid-side shutoff valve22.

The refrigerant sent to the main liquid refrigerant pipe 252 in theconnection unit 200A partially flows to the branching liquid refrigerantpipe 254 and the remaining thereof flows toward the utilizationflow-rate control valve 320 in the utilization unit 300A. Therefrigerant flowing through the main liquid refrigerant pipe 252 towardthe utilization flow-rate control valve 320 is cooled through heatexchange in the subcooling heat exchanger 210 with the refrigerantflowing through the branching liquid refrigerant pipe 254 toward thelow-pressure gas refrigerant pipe 264, and then flows into theutilization flow-rate control valve 320. The refrigerant sent to theutilization flow-rate control valve 320 in the utilization unit 300A isflow-rate controlled by the utilization flow-rate control valve 320 inthe utilization unit 300A and is then evaporated to become alow-pressure gas refrigerant through heat exchange with indoor airsupplied from the indoor fan in the utilization heat exchanger 310 ofthe utilization unit 300A. Meanwhile, the indoor air is cooled and issupplied into the room. The low-pressure gas refrigerant flowing out ofthe utilization heat exchanger 310 is sent to the joined gas refrigerantpipe 266 in the connection unit 200A. The low-pressure gas refrigerantsent to the joined gas refrigerant pipe 266 flows into the low-pressuregas refrigerant pipe 264, and joins the refrigerant flowing from thebranching liquid refrigerant pipe 254 to be sent to the low-pressuregas-refrigerant connection pipe 36. The low-pressure gas refrigerantsent to the low-pressure gas-refrigerant connection pipe 36 returns tothe suction side (the suction pipe 110 a) of the compressor 110 via thelow-pressure gas-side shutoff valve 26.

The refrigerant sent from the liquid-refrigerant connection pipe 32 tothe receiver 180 is temporarily stored in the receiver 180 and thenflows out to be sent to the heat source-side flow-rate control valve150. The refrigerant sent to the heat source-side flow-rate controlvalve 150 is evaporated to become a low-pressure gas refrigerant throughheat exchange with water as the heat source in the heat source-side heatexchanger 140 and is sent to the first flow path switching mechanism132. The low-pressure gas refrigerant sent to the first flow pathswitching mechanism 132 then returns to the suction side (the suctionpipe 110 a) of the compressor 110.

(4) Control to Open or Close First Suction Return Valve

Control to open or close the first suction return valve 162 by thecontrol unit 400 will be described next with reference to a flowchart inFIG. 8. Assume that the first suction return valve 162 is closed whenstep S1 described below starts.

The controller 406 initially determines whether or not the temperaturein the casing 106 measured by the casing internal temperature sensor Tais higher than the predetermined set temperature (step S1). The settemperature may have a value preliminarily stored in the memory of thecontrol unit 400, or a value set by the user of the air conditioner 10with use of the operation unit (not depicted) of the air conditioner 10.The process proceeds to step S2 if the temperature in the casing 106measured by the casing internal temperature sensor Ta is higher than thepredetermined set temperature. Step S1 is repeated until the temperaturein the casing 106 measured by the casing internal temperature sensor Tais determined as being higher than the predetermined set temperature.

Subsequently in step S2, the controller 406 calculates evaporationtemperature in the refrigeration cycle in accordance with theinformation on the relation between temperature and pressure of arefrigerant stored in the memory of the control unit 400 and a lowpressure value in the refrigeration cycle measured by the low pressuresensor P2.

Subsequently in step S3, the controller 406 calculates the quantity A1of a liquid refrigerant evaporable in the cooling heat exchanger 160when the refrigerant is supplied to the cooling heat exchanger 160, inaccordance with the evaporation temperature in the refrigeration cyclecalculated in step S2, the temperature in the casing 106 measured by thecasing internal temperature sensor Ta, and the information on therelation between the quantity of the refrigerant evaporable in thecooling heat exchanger 160 and air temperature in the casing 106 atdifferent evaporation temperature levels in the refrigeration cyclestored in the memory of the control unit 400.

Subsequently in step S4, the controller 406 calculates the pressuredifference ΔP between the first pressure Pr1 and the second pressure Pr2using the first pressure Pr1 derived by the first deriving unit 402 andthe second pressure Pr2 derived by the second deriving unit 404.

Subsequently in step S5, the controller 406 calculates the quantity A2(flow rate) of the refrigerant expected to be supplied to the coolingheat exchanger 160 when the first suction return valve 162 is opened, inaccordance with the pressure difference ΔP calculated in step S4 and theinformation on the relation between pressure difference and a flow rateof a liquid refrigerant stored in the memory of the control unit 400.

Subsequently in step S6, the controller 406 compares the quantity A1 ofthe liquid refrigerant evaporable in the cooling heat exchanger 160 whenthe refrigerant is supplied to the cooling heat exchanger 160 and thequantity A2 of the refrigerant expected to be supplied to the coolingheat exchanger 160 when the first suction return valve 162 is opened.The process proceeds to step S7 if the quantity A2≤the quantity A1 isestablished. If the quantity A2>the quantity A1 is established, thecontroller 406 keeps the first suction return valve 162 closed (i.e.does not open the first suction return valve 162), and the processreturns to step S2.

In step S7, the controller 406 opens the first suction return valve 162.The process subsequently proceeds to step S8.

In step S8, the controller 406 determines whether or not the temperaturein the casing 106 measured by the casing internal temperature sensor Tais less than a value obtained by subtracting a value α from thepredetermined set temperature. The value α has a predetermined positivevalue. Although the value α may alternatively be zero, the value αhaving an appropriate positive value leads to preventing the firstsuction return valve 162 from frequently opening and closing. When thetemperature in the casing 106 is less than the value obtained bysubtracting the value α from the set temperature, the process proceedsto step S9. The processing in step S8 is repeated until the temperaturein the casing 106 is assessed as being less than the value obtained bysubtracting the value α from the set temperature.

In step S9, the controller 406 closes the first suction return valve162. The process subsequently returns to step S1.

(5) Characteristics

(5-1)

The air conditioner 10 exemplifying the refrigeration apparatusaccording to the embodiment described above includes the heat sourceunit 100, the utilization unit 300, and the controller 406. The heatsource unit 100 includes the compressor 110, the heat source-side heatexchanger 140 exemplifying the main heat exchanger, the casing 106, thecooling heat exchanger 160, and the first suction return valve 162. Thecompressor 110 compresses a refrigerant. The heat source-side heatexchanger 140 causes heat exchange between the refrigerant and a heatsource. The casing 106 accommodates the compressor 110 and the heatsource-side heat exchanger 140. The cooling heat exchanger 160 issupplied with the refrigerant to cool the interior of the casing 106.The first suction return valve 162 switches to supply or not to supplythe cooling heat exchanger 160 with the refrigerant. The utilizationunit 300 includes the utilization heat exchanger 310. The utilizationunit 300 and the heat source unit 100 constitute the refrigerant circuit50. The controller 406 controls to open or close the first suctionreturn valve 162. The controller 406 assesses, before the first suctionreturn valve 162 is opened to supply the cooling heat exchanger 160 withthe refrigerant, whether or not the refrigerant flowing from the coolingheat exchanger 160 toward the compressor 110 comes into the wet statewhen the refrigerant is supplied to the cooling heat exchanger 160, anddetermines whether or not to open the first suction return valve 162 inaccordance with an assessment result.

In the present air conditioner 10, it is determined whether to open ornot to open the first suction return valve 162 for switching betweensupply and non-supply of the refrigerant to the cooling heat exchanger160 in accordance with the assessment result as to whether or not therefrigerant that flows from the cooling heat exchanger 160 used to coolthe interior of the casing 106 toward the compressor 110 will come intothe wet state. This configuration achieves a highly reliable airconditioner 10 that can reduce the liquid compression caused by supplyof the refrigerant to the cooling heat exchanger 160.

(5-2)

In the air conditioner 10 according to the above embodiment, thecontroller 406 assesses whether or not the refrigerant flowing out ofthe cooling heat exchanger 160 entirely comes into the gaseous statewhen the refrigerant is supplied to the cooling heat exchanger 160, anddetermines whether or not to open the first suction return valve 162 inaccordance with an assessment result.

In the present air conditioner 10, whether or not to open the firstsuction return valve 162 configured to switch to supply or not to supplythe cooling heat exchanger 160 with the refrigerant is determined inaccordance with the assessment result as to whether or not therefrigerant immediately after flowing out of the cooling heat exchanger160 entirely comes into the gaseous state. This configuration thusparticularly facilitates reduction of liquid compression caused bysupply of the refrigerant to the cooling heat exchanger 160.

(5-3)

The air conditioner 10 according to the above embodiment includes thefirst deriving unit 402 and the second deriving unit 404. The firstderiving unit 402 derives the first pressure Pr1 upstream of the firstsuction return valve 162 in the refrigerant flow direction F of therefrigerant flowing to the cooling heat exchanger 160 when the firstsuction return valve 162 is opened. The second deriving unit 404 derivesthe second pressure Pr2 downstream of the cooling heat exchanger 160 inthe refrigerant flow direction F. The controller 406 determines whetheror not to open the first suction return valve 162 in accordance with thepressure difference ΔP between the first pressure Pr1 and the secondpressure Pr2.

In the present air conditioner 10, whether or not to open the firstsuction return valve 162 is determined in accordance with a highlyaccurate assessment result with reference to the pressure difference ΔPbetween the first pressure Pr1 and the second pressure Pr2 correlatedwith quantity of the refrigerant flowing in the cooling heat exchanger160 when the first suction return valve 162 is opened. The airconditioner 10 thus achieves high reliability in which the occurrence ofliquid compression can be reduced.

(5-4)

The air conditioner 10 according to the above embodiment includes thecasing internal temperature sensor Ta exemplifying a temperaturemeasurement unit. The casing internal temperature sensor Ta measurestemperature in the casing 106. The controller 406 determines whether ornot to open the first suction return valve 162 in accordance with thetemperature in the casing 106.

In the present air conditioner 10, whether or not to open the firstsuction return valve 162 is determined in accordance with highlyaccurate assessment as to whether or not the refrigerant flowing fromthe cooling heat exchanger 160 toward the compressor 110 comes into thewet state when the refrigerant is supplied to the cooling heat exchanger160, with reference to the temperature in the casing 106 correlated withquantity of heat supplied to the refrigerant in the cooling heatexchanger 160. The air conditioner 10 thus achieves high reliability inwhich the occurrence of liquid compression can be reduced.

(5-5)

In the air conditioner 10 according to the above embodiment, the coolingheat exchanger 160 is disposed on the first suction return pipe 160 aconnecting the pipe connecting between the heat source-side heatexchanger 140 and the utilization heat exchanger 310 and the suctionpipe 110 a of the compressor 110.

The present air conditioner 10 achieves high reliability so as to reducethe occurrence of liquid compression caused by the refrigerant flowingfrom the cooling heat exchanger 160 to the suction pipe 110 a.

(5-6)

In the air conditioner 10 according to the above embodiment, the heatsource of the heat source unit 100 is water.

The air conditioner 10 thus can achieve control of the temperature inthe casing 106 at predetermined temperature even in a case where the airconditioner 10 utilizes water as the heat source and is likely to haveheat accumulated in the casing 106

(6) Modification Examples

The modification examples of the above embodiment will be describedhereinafter. Any of the following modification examples may be combinedwhere appropriate within a range causing no contradiction.

(6-1) Modification Example A

According to the above embodiment, the controller 406 in the controlunit 400 assesses whether or not the refrigerant immediately afterflowing out of the cooling heat exchanger 160 entirely comes into thegaseous state when the refrigerant is supplied to the cooling heatexchanger 160, and determines whether or not to open the first suctionreturn valve 162 in accordance with an assessment result. The presentinvention should not be limited to this configuration, but the airconditioner may alternatively be configured in the following manner.

An air conditioner according to the modification example A includes acontrol unit 400 a in place of the control unit 400. The air conditioneraccording to the modification example A is physically configuredsimilarly to the air conditioner 10 according to the above embodiment,and operates similarly to the air conditioner 10 according to the aboveembodiment except for control of the first suction return valve 162 bythe control unit 400 a. Description is accordingly made herein to onlythe control of the first suction return valve 162 by the control unit400 a, and the remaining features will not be described repeatedly.

The control unit 400 a includes a microcomputer having, as functionalunits relevant to control to open or close the first suction returnvalve 162, the first deriving unit 402, the second deriving unit 404, acontroller 406 a, and a superheating degree deriving unit 408 asdepicted in FIG. 5. The first deriving unit 402 and the second derivingunit 404 are configured similarly to those according to the aboveembodiment and thus will not be described repeatedly.

The controller 406 a according to the modification example A assesseswhether or not the refrigerant that is obtained after mixing therefrigerant flowing out of the cooling heat exchanger 160 and therefrigerant returning from the utilization unit 300 and that flowstoward the compressor 110 comes into the wet state when the refrigerantis supplied to the cooling heat exchanger 160, and determines whether ornot to open the first suction return valve 162 in accordance with anassessment result. The refrigerant returning from the utilization unit300 and flowing toward the compressor 110 includes the refrigerantflowing from the utilization heat exchanger 310 into the suction pipe110 a without passing through any other heat exchanger, and also therefrigerant flowing from the utilization heat exchanger 310 into thesuction pipe 110 a via the heat source-side heat exchanger 140.

According to the above embodiment, whether or not the refrigerantimmediately after flowing out of the cooling heat exchanger 160 entirelycomes into the gaseous state when the refrigerant is supplied to thecooling heat exchanger 160 is assessed in order for assessment as towhether or not the refrigerant flowing from the cooling heat exchanger160 toward the compressor 110 comes into the wet state when therefrigerant is supplied to the cooling heat exchanger 160. In contrast,according to the modification example A, if the refrigerant that isobtained after mixing the refrigerant flowing out of the cooling heatexchanger 160 and the refrigerant returning from the utilization unit300 and that flows toward the compressor 110 is assessed as not cominginto the wet state, the refrigerant flowing from the cooling heatexchanger 160 toward the compressor 110 is assessed as not coming intothe wet state even in a case where the refrigerant is supplied to thecooling heat exchanger 160 and the refrigerant immediately after flowingout of the cooling heat exchanger 160 does not entirely come into thegaseous state (comes into the wet state). Assessment by the controller406 a will be described later.

The superheating degree deriving unit 408 derives a degree ofsuperheating of the refrigerant returning from the utilization unit 300to the suction pipe 110 a. The superheating degree deriving unit 408derives the degree of superheating of the refrigerant returning from theutilization unit 300 to the suction pipe 110 a in the followingexemplary manner.

Assume an exemplary case where the utilization units 300A and 300B bothexecute cooling operation (where the utilization heat exchangers 310each function as an evaporator).

The superheating degree deriving unit 408 calculates a degree ofsuperheating of the refrigerant returning from the utilization unit 300Ato the suction pipe 110 a with reference to the liquid-side temperaturesensor T5 a and the gas-side temperature sensor T6 a in the utilizationunit 300A (by subtracting temperature measured by the liquid-sidetemperature sensor T5 a from temperature measured by the gas-sidetemperature sensor T6 a). The superheating degree deriving unit 408 alsocalculates a degree of superheating of the refrigerant returning fromthe utilization unit 300B to the suction pipe 110 a with reference tothe liquid-side temperature sensor T5 b and the gas-side temperaturesensor T6 b in the utilization unit 300B. Quantity balance between therefrigerants supplied to the utilization heat exchangers 310 in theutilization units 300A and 300B can be assessed in accordance withcapacity of the utilization heat exchanger 310 in the utilization unit300A and capacity of the utilization heat exchanger 310 in theutilization unit 300B. The superheating degree deriving unit 408 canthus calculate the degree of superheating of the refrigerant returningfrom each of the utilization units 300 to the suction pipe 110 a inaccordance with the capacity of the utilization units 300A and 300Bstored in the memory of the control unit 400 and the degree ofsuperheating of the refrigerant at the outlet of the utilization heatexchanger 310 in each of the utilization units 300A and 300B. Assumingthat the utilization unit 300B has capacity (horsepower) two times ofcapacity of the utilization unit 300A, the superheating degree derivingunit 408 can calculate the degree of superheating of the refrigerantreturning from each of the utilization units 300 to the suction pipe 110a through calculation of (the degree of superheating in the utilizationunit 300A+ the degree of superheating in the utilization unit 300B×2)/3.

Assume another case where the utilization units 300A and 300B bothexecute heating operation (where the utilization heat exchangers 310each function as a radiator).

In this case, the superheating degree deriving unit 408 calculates thedegree of superheating of the refrigerant returning from each of theutilization units 300 to the suction pipe 110 a with reference to theliquid-side temperature sensor T4 and the gas-side temperature sensor T3in the heat source unit 100A (by subtracting temperature measured by theliquid-side temperature sensor T4 from temperature measured by thegas-side temperature sensor T3).

Control to open or close the first suction return valve 162 by thecontrol unit 400 a will be described next with reference to flowchartsin FIG. 10 and FIG. 11.

Control to open or close the first suction return valve 162 by thecontrol unit 400 a flows similarly to the process of control depicted inFIG. 8 and described in the above embodiment, except that, if thequantity A2 of the refrigerant expected to be supplied to the coolingheat exchanger 160 when the first suction return valve 162 is opened islarger than the quantity A1 of the liquid refrigerant evaporable in thecooling heat exchanger 160 when the refrigerant is supplied to thecooling heat exchanger 160 in step S6, the process does not returndirectly to step S2 but proceeds to step S10 and step S20, and theprocess may proceed to step S7 in accordance with a determination resultin step S20. Description is accordingly made to only step S10 and stepS20.

If the quantity A2 of the refrigerant expected to be supplied to thecooling heat exchanger 160 when the first suction return valve 162 isopened is determined as being more than the quantity A1 of the liquidrefrigerant evaporable in the cooling heat exchanger 160 when therefrigerant is supplied to the cooling heat exchanger 160 in step S6,the process proceeds to step S10

In step S10, the control unit 400 a calculates an expected degree ofsuperheating of the refrigerant at the suction side of the compressor110 when the refrigerant is supplied to the cooling heat exchanger 160.Such processing in step S10 will be described in detail with referenceto the flowchart in FIG. 11.

In step S11, the controller 406 a calculates quantity (expectedquantity) of the refrigerant not evaporating in the cooling heatexchanger 160 and flowing into the suction pipe 110 a when therefrigerant is supplied to the cooling heat exchanger 160. Specifically,the controller 406 a calculates the quantity of the refrigerant notevaporating in the cooling heat exchanger 160 and flowing into thesuction pipe 110 a by subtracting the quantity A1 of the liquidrefrigerant evaporable in the cooling heat exchanger 160 when therefrigerant is supplied to the cooling heat exchanger 160 from thequantity A2 of the refrigerant expected to be supplied to the coolingheat exchanger 160 when the first suction return valve 162 is opened.

Subsequently in step S12, the controller 406 a calculates quantity ofthe refrigerant returning from each of the utilization units 300 to thesuction pipe 110 a in accordance with the number of rotations of thecompressor 110, the opening degrees of the flow-rate control valves 150and 320, or the like. Specifically, the control unit 400 a includes amemory storing information on a relation between quantity of therefrigerant circulating in the refrigerant circuit 50 and the number ofrotations of the compressor 110, the opening degrees of the flow-ratecontrol valves 150 and 320, and the like. The controller 406 acalculates quantity of the refrigerant circulating in the refrigerantcircuit 50 in accordance with the number of rotations of the compressor110, the opening degrees of the flow-rate control valves 150 and 320, orthe like, with reference to the information stored in the memory of thecontrol unit 400 a. The controller 406 a further calculates the quantityof the refrigerant returning from each of the utilization units 300 tothe suction pipe 110 a by subtracting, from the quantity of therefrigerant circulating in the refrigerant circuit 50, quantity of therefrigerant bypassing the second suction return pipe 170 a or the likeand flowing into the suction pipe 110 a (e.g. quantity of therefrigerant calculated from the opening degree of the second suctionreturn valve 172 and the pressure difference ΔP between the firstpressure Pr1 and the second pressure Pr2). In a case where therefrigerant does not flow through the second suction return pipe 170 aor the like (where the refrigerant does not bypass), the controller 406a may regard the quantity of the refrigerant circulating in therefrigerant circuit 50 as the quantity of the refrigerant returning fromeach of the utilization units 300 to the suction pipe 110 a.

Subsequently in step S13, the superheating degree deriving unit 408calculates a degree of superheating of the refrigerant returning fromthe utilization unit 300 to the suction pipe 110 a.

Subsequently in step S14, the controller 406 a assesses whether or notthe refrigerant that is obtained after mixing the refrigerant flowingout of the cooling heat exchanger 160 and the refrigerant returning fromthe utilization unit 300 and that flows toward the compressor 110 comesinto the wet state in accordance with the degree of superheating and thequantity of the refrigerant returning from each of the utilization units300 to the suction pipe 110 a, quantity of heat needed to evaporate theliquid refrigerant of the quantity calculated in step S11, or the like.Specifically in this case, the controller 406 a calculates the degree ofsuperheating (the expected degree of superheating) of the refrigerantthat is obtained after mixing the refrigerant flowing out of the coolingheat exchanger 160 and the refrigerant returning from the utilizationunit 300 and that flows toward the compressor 110 when the refrigerantis supplied to the cooling heat exchanger 160.

The control unit 400 a then completes the processing in step S10.

Subsequently in step S20, the controller 406 a compares the expecteddegree of superheating calculated in step S10 (step S14) with a targetdegree of superheating, assesses that the refrigerant flowing from thecooling heat exchanger 160 toward the compressor 110 (after joining therefrigerant flowing from the utilization unit 300 toward the compressor110) does not come into the wet state in a case where the expecteddegree of superheating is equal to or more than the target degree ofsuperheating, and determines to open the first suction return valve 162.The process then proceeds to step S7. In another case where the expecteddegree of superheating is less than the target degree of superheating,the controller 406 keeps the first suction return valve 162 closed (i.e.does not open the first suction return valve 162). The process thenproceeds to step S2. The target degree of superheating preferably has apositive value, or may alternatively be zero.

In the air conditioner according to the modification example A, thecontroller 406 a assesses whether or not the refrigerant that isobtained after mixing the refrigerant flowing out of the cooling heatexchanger 160 and the refrigerant returning from the utilization unit300 and that flows toward the compressor 110 comes into the wet statewhen the refrigerant is supplied with the cooling heat exchanger 160,and determines whether or not to open the first suction return valve 162in accordance with an assessment result.

In this case, whether or not to open the first suction return valve 162configured to switch to supply or not to supply the cooling heatexchanger 160 with the refrigerant is determined in accordance with theassessment result as to whether or not the refrigerant that is obtainedafter mixing the refrigerant flowing out of the cooling heat exchanger160 and the refrigerant returning from the utilization unit 300 and thatflows toward the compressor 110 comes into the wet state. The coolingheat exchanger 160 may thus be occasionally supplied with therefrigerant even under the condition where the refrigerant immediatelyafter flowing out of the cooling heat exchanger 160 comes into the wetstate. The cooling heat exchanger 160 in the present air conditioner 10is accordingly applicable under a wider condition.

The air conditioner according to the modification example A includes thefirst deriving unit 402 and the second deriving unit 404. The firstderiving unit 402 derives the first pressure Pr1 upstream of the firstsuction return valve 162 in the refrigerant flow direction F of therefrigerant flowing to the cooling heat exchanger 160 when the firstsuction return valve 162 is opened. The second deriving unit 404 derivesthe second pressure Pr2 downstream of the cooling heat exchanger 160 inthe refrigerant flow direction F. The controller 406 a determineswhether or not to open the first suction return valve 162 in accordancewith the pressure difference ΔP between the first pressure Pr1 and thesecond pressure Pr2 and the quantity of the refrigerant returning fromthe utilization unit 300.

In this case, whether or not to open the first suction return valve 162is determined in accordance with highly accurate assessment as towhether or not the refrigerant flowing toward the compressor 110 comesinto the wet state with reference to the pressure difference ΔP betweenthe first pressure Pr1 and the second pressure Pr2 correlated with thequantity of the refrigerant flowing in the cooling heat exchanger 160when the first suction return valve 162 is opened, as well as thequantity of the refrigerant returning from the utilization unit 300. Theair conditioner 10 thus achieves high reliability in which theoccurrence of liquid compression can be reduced.

The modification example A provides a refrigeration apparatus includingthe casing internal temperature sensor Ta and the superheating degreederiving unit 408. The casing internal temperature sensor Ta measurestemperature in the casing 106. The superheating degree deriving unit 408derives the degree of superheating of the refrigerant returning from theutilization unit 300. The controller 406 a determines whether or not toopen the first suction return valve 162 in accordance with thetemperature in the casing 106 and the degree of superheating of therefrigerant returning from the utilization unit 300.

In this case, whether or not to open the first suction return valve 162is determined in accordance with highly accurate assessment as towhether or not the refrigerant flowing toward the compressor 110 comesinto the wet state with reference to the temperature in the casing 106correlated with the quantity of heat supplied to the refrigerant in thecooling heat exchanger 160 as well as the degree of superheating of therefrigerant returning from the utilization unit 300. The air conditioner10 thus achieves high reliability in which the occurrence of liquidcompression can be reduced.

(6-2) Modification Example B

The modification example A provides calculation of the degree ofsuperheating of the refrigerant returning from each of the utilizationunits 300 to the suction side of the compressor 110 in accordance withthe degree of superheating at outlets of the utilization heat exchanger310 in each of the utilization units 300A and 300B and the heatsource-side heat exchanger 140 in the heat source unit 100A as well asthe quantity balance between the refrigerants flowing in the heatexchangers 310 and 140. The present invention should not be limited tothis configuration.

For example, the superheating degree deriving unit 408 may alternativelycalculate the degree of superheating of the refrigerant returning fromthe utilization unit 300 to the suction side of the compressor 110 inaccordance with the sucked refrigerant temperature sensor T2 providedadjacent to an inlet of the accumulator 124 and the evaporationtemperature in the refrigeration cycle obtained from measurement valuesof the low pressure sensor P2. This case enables calculation of acurrent degree of superheating of the refrigerant flowing into thecompressor 110 inclusive of the refrigerant bypassing the second suctionreturn pipe 170 a or the like and flowing into the suction pipe 110 a.The controller 406 a can calculate a degree of superheating (an expecteddegree of superheating) of the refrigerant that is obtained after mixingthe refrigerant flowing out of the cooling heat exchanger 160 and therefrigerant returning from the utilization unit 300 and that flowstoward the compressor 110 when the refrigerant is supplied to thecooling heat exchanger 160, in accordance with the current degree ofsuperheating of the refrigerant flowing into the compressor 110, currentquantity of the refrigerant circulating in the refrigerant circuit 50calculated from the number of rotations of the compressor 110, theopening degrees of the flow-rate control valves 150 and 320, or thelike, and quantity of the refrigerant not evaporating in the coolingheat exchanger 160 and flowing into the suction pipe 110 a when therefrigerant is supplied to the cooling heat exchanger 160.

(6-3) Modification Example C

The heat source unit 100 according to the above embodiment utilizeswater as the heat source. The present invention should not be limited tothis configuration. The heat source of the heat source unit 100 mayalternatively be air.

(6-4) Modification Example D

The air conditioner 10 according to the above embodiment includes theconnection units 200, to allow part of the utilization units 300 toexecute cooling operation and allow the remaining utilization unit 300to execute heating operation. The present invention should not belimited to this configuration. The air conditioner exemplifying therefrigeration apparatus according to the present invention may not beconfigured to execute simultaneous cooling and heating operation.

(6-5) Modification Example E

The cooling heat exchanger 160 according to the above embodiment issupplied with air having cooled the electric components 104. The presentinvention should not be limited to this configuration. The airconditioner 10 may further include a fan provided separately from thefan 166 configured to guide air to the electric components 104, and thefan may be configured to supply the cooling heat exchanger 160 with airin the casing 106.

(6-6) Modification Example F

The first suction return pipe 160 a according to the above embodiment isprovided with the first suction return valve 162 configured as anelectromagnetic valve and the capillary 164. In the case where the firstsuction return pipe 160 a is provided with the motor valve having acontrollable opening degree in place of the first suction return valve162 and the capillary 164, the memory of the control unit 400 preferablystores information on a relation between the pressure difference ΔPbetween the first pressure Pr1 and the second pressure Pr2 when themotor valve is controlled to have a predetermined opening degree, and aflow rate of a liquid refrigerant flowing in the cooling heat exchanger160, and the controller 406 preferably calculates a flow rate from thecalculated pressure difference ΔP in accordance with the information.

(6-7) Modification Example G

If the refrigerant flowing from the cooling heat exchanger 160 towardthe compressor 110 is assessed as being in the wet state in accordancewith a sensor measurement result after the first suction return valve162 is opened in step S7 in the flowchart in FIG. 8, the controller 406may be configured to close the first suction return valve 162 even in acase where a condition in step S8 is not satisfied.

(6-8) Modification Example H

The controller 406 according to the above embodiment assesses whether ornot the refrigerant comes into the wet state before the cooling heatexchanger 160 is used. The controller 406 may assess the wet state inaccordance with a method similar to the assessment method describedabove after the first suction return valve 162 is opened to use thecooling heat exchanger 160, and may adopt an assessment result as acondition for closing the first suction return valve 162.

In this case, the first suction return valve 162 may be controlled toclose not in accordance with the above assessment method but inaccordance with a degree of superheating obtained as a differencebetween a measurement value of a temperature sensor provided downstreamof the cooling heat exchanger 160 (provided on the first suction returnpipe 160 a and downstream of the cooling heat exchanger 160 in therefrigerant flow direction F) and low-pressure saturation temperature ofthe refrigerant (e.g. low-pressure saturation temperature calculatedfrom the measurement value of the low pressure sensor P2). Specifically,the controller 406 may control to close the first suction return valve162 when the degree of superheating as the difference between themeasurement value of the temperature sensor provided downstream of thecooling heat exchanger 160 and the low-pressure saturation temperatureof the refrigerant is equal to or less than a predetermined value.

INDUSTRIAL APPLICABILITY

The present invention provides a highly reliable refrigeration apparatusthat can reduce the cause of the liquid compression.

REFERENCE SIGNS LIST

-   10 air conditioner (refrigeration apparatus)-   50 refrigerant circuit-   100(100A,100B) heat source unit-   106 casing-   110 compressor-   110 a suction pipe-   140 heat source-side heat exchanger (main heat exchanger)-   160 cooling heat exchanger-   160 a first suction return pipe (pipe)-   162 first suction return valve (valve)-   300(300A,300B) utilization unit-   310 utilization heat exchanger-   402 first deriving unit-   404 second deriving unit-   406, 406 a controller-   408 superheating degree deriving unit-   Pr1 first pressure-   Pr2 second pressure-   ΔP pressure difference (pressure difference between first pressure    and second pressure)-   Ta casing internal temperature sensor (temperature measurement unit)

CITATION LIST Patent Literature

Patent Literature 1: JPH8-049884 A

The invention claimed is:
 1. A refrigeration apparatus comprising: aheat source unit including a compressor configured to compress arefrigerant, a main heat exchanger configured to cause heat exchangebetween the refrigerant and a heat source, a casing accommodating thecompressor and the main heat exchanger, a cooling heat exchangersupplied with the refrigerant and configured to cool an interior of thecasing, and a valve configured to switch to supply or not to supply thecooling heat exchanger with the refrigerant; a utilization unitincluding a utilization heat exchanger, the utilization unit and theheat source unit constituting a refrigerant circuit; a first sensorconfigured to detect a temperature or a pressure of the refrigerantflowing in the refrigerant circuit upstream of the valve in arefrigerant flowing direction flowing to the cooling heat exchanger whenthe valve is opened; a second sensor configured to detect a temperatureor a pressure of the refrigerant flowing in the refrigerant circuitdownstream of the cooling heat exchanger in the refrigerant flowingdirection; and a controller configured to control to open or close thevalve, wherein the controller is configured to: derive first pressureupstream of the valve in the refrigerant flow direction, based on adetection result of the first sensor in accordance with information on arelation between temperature and pressure of a refrigerant stored in amemory of the controller in a case where the first sensor is atemperature sensor or based on a detection result of the first sensor ina case where the first sensor is a pressure sensor; derive secondpressure downstream of the cooling heat exchanger in the refrigerantflow direction, based on a detection result of the second sensor inaccordance with information on a relation between temperature andpressure of a refrigerant stored in a memory of the controller in a casewhere the second sensor is a temperature sensor or based on a detectionresult of the first sensor in a case where the second sensor is apressure sensor; assess, before the valve is opened to supply thecooling heat exchanger with the refrigerant, whether or not therefrigerant flowing from the cooling heat exchanger toward thecompressor comes into a wet state when the refrigerant is supplied tothe cooling heat exchanger based on a pressure difference between thefirst pressure and the second pressure; and determine whether or not toopen the valve in accordance with an assessment result.
 2. Therefrigeration apparatus according to claim 1, wherein the controller isfurther configured to: assess whether or not the refrigerant supplied tothe cooling heat exchanger entirely comes into a gaseous stateimmediately after flowing out of the cooling heat exchanger based on thepressure difference between the first pressure and the second pressure;and determine whether or not to open the valve in accordance with theassessment result.
 3. The refrigeration apparatus according to claim 1,further comprising a temperature sensor configured to measuretemperature in the casing, wherein the controller is further configuredto determine whether or not to open the valve also in accordance withthe temperature detected by the temperature sensor.
 4. The refrigerationapparatus according to claim 1, wherein the controller is furtherconfigured to: assess whether or not the refrigerant that is obtainedafter mixing the refrigerant flowing out of the cooling heat exchangerand the refrigerant returning from the utilization unit and that flowstoward the compressor comes into the wet state when the refrigerant issupplied with the cooling heat exchanger based on the pressuredifference between the first pressure and the second pressure and thequantity of the refrigerant returning from the utilization unit; anddetermine whether or not to open the valve in accordance with anassessment result.
 5. The refrigeration apparatus according to claim 4,further comprising: a temperature sensor configured to measuretemperature in the casing, wherein the controller is further configuredto: derive a degree of superheating of the refrigerant returning fromthe utilization unit based on the detection result of the temperaturesensor; and determine whether or not to open the valve also inaccordance with the temperature and the degree of superheating.
 6. Therefrigeration apparatus according to claim 1, wherein the cooling heatexchanger is disposed on a pipe connecting a pipe connecting between themain heat exchanger and the utilization heat exchanger and a suctionpipe of the compressor.
 7. The refrigeration apparatus according toclaim 1, wherein the heat source is water.